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Gastrointestinal stromal tumours: An update
ARTICLE IN PRESS Current Diagnostic Pathology (2005) 11, 400–410
www.elsevier.com/locate/cdip
MINI-SYMPOSIUM: BONE AND SOFT TISSUE PATHOLOGY
Gastrointestinal stromal tumours: An update Muna Sabah, Mary Leader, Elaine Kay Department of Histopathology, Education and Research Centre, Beaumont Hospital and Royal College of Surgeons in Ireland, Dublin 9, Ireland
KEYWORDS GIST; KIT; Morphology; Prognosis
Summary Gastrointestinal stromal tumours (GISTs) comprise the largest subset of mesenchymal tumours of the digestive tract. These tumours have been the subject of considerable debate in the literature regarding their histogenesis, criteria for diagnosis, prognostic features and biological behaviour. The majority of GISTs express CD117 immunostaining and show various degrees of differentiation towards the phenotype of interstitial cell of Cajal. Clinically and histologically, GISTs represent a spectrum that includes benign and malignant variants. The prediction of clinical behaviour is best achieved by evaluation of multiple parameters including clinical, morphological and cytogenetic features. The recognition of the central role played by activating mutations of c-kit and platelet derived growth factor receptor alpha in the pathogenesis of GISTs and the introduction of STI-571, a receptor tyrosine kinase inhibitor that has proved extremely effective in the treatment of GISTs, have not only have focused attention on these tumours but also made it necessary to accurately define these tumours and separate them from other mesenchymal lesions. This review discusses the definition, histogenesis, epidemiology, clinical presentation, morphological and immunohistochemical features and the differential diagnosis of GISTs and addresses predictors of malignancy and management of GISTs. & 2005 Elsevier Ltd. All rights reserved.
Historical overview: from Stout to molecular revolution The first accurate description of mesenchymal neoplasms of the gastrointestinal (GI) tract was in 1941.1 Traditionally, these tumours were thought to Corresponding author. Tel.: +353 1 809 2541;
fax: +353 1 809 3720. E-mail address: [email protected] (M. Sabah).
be derived from smooth muscle cells, based on their resemblance to smooth muscle tumours and they were designated as leiomyomas, bizarre leiomyomas,2 cellular leiomyomas3 and leiomyosarcomas. However, with the advent of electron microscopy, it has been shown that relatively few neoplasms showed convincing ultrastructural evidence of smooth muscle differentiation. The application of immunohistochemistry revealed that many of these neoplasms lacked the immunophenotypical features
0968-6053/$ - see front matter & 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.cdip.2005.08.003
ARTICLE IN PRESS Gastrointestinal stromal tumours of smooth muscle differentiation. This led Mazur and Clark4 in 1983 to introduce the generic designation ‘stromal tumour’. Subsequently, Herrera et al.5 introduced the concept of ‘plexosarcoma’ in 1984 to acknowledge the existence of a small subset of stromal tumours with autonomic neuronal differentiation which became better known as gastrointestinal autonomic nerve tumours (GANTs).6 There was considerable controversy as to the line of differentiation, since some tumours exhibited a myogenic phenotype, others showed neural differentiation, some revealed mixed differentiation and some cases did not show any specific line of differentiation, the ‘null phenotype’. Some enthusiasm was generated by the recognition that a significant proportion of stromal tumours express CD34.7 However, the diagnostic utility of this marker was hampered by its poor specificity. As a consequence of the lack of reproducible diagnostic criteria, gastrointestinal stromal tumour (GIST) represented a generic term to indicate any mesenchymal tumour arising in the GI tract. The recognition of the central role of c-kit mutations in the pathogenesis of GISTs8,9 and, in most cases, the associated expression of KIT protein in these tumours has provided a reproducible genotypic and phenotypic marker.10 Therefore, KIT (CD117 in the standardized terminology of leucocyte antigens) expression has emerged as a marker for discriminating GISTs from other mesenchymal GI neoplasms and some have equated immunoreactivity for KIT as the definition of GISTs.11 Recently, it has become apparent that some GISTs that lacked c-kit mutations were found to have activating mutations of platelet derived growth factor receptor (PDGFRA). Therefore, the definition of GISTs may need to be revised. GISTs may now be considered to encompass mesenchymal tumours that express KIT protein or have activating mutations of receptor tyrosine kinase genes (c-kit or platelet derived growth factor receptor alpha (PDGFRA)). However, for most clinical purposes, GISTs may simply be referred to as KIT-positive tumours with appropriate morphology, although this definition is somewhat inaccurate.
401 smooth muscle cells. Their principal function is to generate autonomous rhythmic contractions, involved in digestion and peristalsis. Therefore, these cells are known as GI ‘pacemaker’ cells. Immunohistochemical studies revealed that GISTs have similar features to ICC, being positive with CD34 and CD117 and negative or variably positive for other neural and smooth muscle markers.10
Molecular biology (c-kit and PDGFRA mutations) The c-kit proto-oncogene, located on the long arm of chromosome 4, encodes a class III transmembrane tyrosine kinase receptor.12 KIT protein consists of an extracellular ligand-binding site and an intracellular kinase domain. The ligand for KIT is a growth factor called the stem cell factor. Extracellular binding of stem cell factor results in dimerization of the receptor, triggering phosphorylation of the kinase domain. This induces a signalling cascade that propagates through the cytoplasm into the nucleus. This signalling cascade affects many aspects of cellular behaviour including proliferation, differentiation, adhesion and apoptosis.12 KIT expression is extremely important in the development of several cell types including haematopoietic stem cells, mast cells, germ cells, melanocytes, some epithelial cells and the ICC.12 Gains of function mutations of c-kit have been observed in sporadic GISTs and, less commonly, as germline mutations in familial GISTs,8,13 suggesting that constitutive expression of KIT plays a significant role in the tumourigenesis of GISTs. The most common mutations are in the juxtamembrane
Histogenesis It has been suggested that GISTs originate from the interstitial cell of Cajal (ICC), or from a primitive stem cell that differentiates towards both the ICC and smooth muscle phenotye.9,10 The ICCs are intercalated between the autonomic nerves and
Figure 1 c-kit mutations in the juxtamembrane cellular domain of exon 11 are seen in 71% of GISTs. Mutations in the extracellular domain of exon 9 and mutations in the tyrosine kinase domain on exons 13 and 17 are less common. Modified from Heinrich et al.14
ARTICLE IN PRESS 402 region in exon 11, resulting in ligand-independent activation of the tyrosine kinase activity.8 Mutations in exon 9 (extracellular domain) and rarely in exon 13 (kinase domain) or 17 (the phosphotransferase domain) can be detected (Fig. 1).14 However, around 10–15% of GISTs lack KIT expression.15 Within this group a large subset would have gain of function mutations of PDGFRA.16 Mutations in PDGFRA provide an alternative mechanism in GIST oncogenesis.
Epidemiology and risk factors The lack of accepted diagnostic criteria for GISTs has led to variation in the current estimate of disease incidence. GIST is a relatively rare neoplasm representing less than 1% of all primary tumours of the GI tract with an incidence of approximately 10–20/million.11 Disease incidence appears to be uniform across all geographical and ethnic populations. GISTs predominantly arise in the middle aged or elderly and are rare in young adults. The median age is around 60 years. There is no gender preference except in the setting of Carney17 triad (malignant gastric epithelioid stromal tumour, pulmonary chondroma and functioning extra-adrenal paraganglioma), nearly all of which occur in females. There are no known risk factors; however, genetic influence has been described, including reports of familial GISTs13 and GISTs in association with von Recklinghausen’s disease.18
Clinical presentation GISTs present a spectrum from clinically benign tumours to sarcomas. The symptoms vary according to the size and location of the tumour. Small tumours are asymptomatic and found incidentally at laparotomy, endoscopy or during radiological studies for other conditions. Symptomatic tumours often present with abdominal discomfort. They may ulcerate and present with GI bleeding. Lesions in the oesophagus may present with dysphagia, while intestinal neoplasms may present with abdominal mass, obstruction or perforation. Some patients present with metastases, particularly to the liver. GISTs occur at every level of the GI tract. Most tumours arise in the stomach (60%) and about 20–30% occur in the small intestine. Colorectal and oesophageal GISTs account for less than 10%.11 A small proportion of GISTs arise in extra-GI tract sites including the omentum, mesentery and retroperitoneum.
M. Sabah et al.
Morphology Gross features GISTs range in size from several millimetres to over 30 cm. Most lesions are well circumscribed, but unencapsulated. Some are multi-nodular. They may have a whorled fibroid-like cut surface or they may be fleshy in appearance. Areas of haemorrhage, cystic degeneration and central necrosis may be seen. GISTs tend to be primarily intramural tumours, usually involving the submucosa and muscularis propria. Large tumours may have a dumbbell appearance with the tumour protruding both into the lumen and from the serosa.
Microscopic features GISTs show a spectrum of histological features. Morphologically, the cells of GISTs are spindle, epithelioid, mixed pattern and occasionally pleomorphic. Spindle cell type is the predominant pattern, seen in 70% of GIST cases (Fig. 2(A)). The tumour cells are arranged in short fascicles, whorls or a storiform growth pattern. The neoplastic cells have light fibrillary eosinophilic cytoplasm with indistinct cell borders. Perinuclear vacuoles are present and indent the nucleus at one pole (Fig. 2(B)). These vacuoles are an artefact of fixation since they are not present in frozen sections.3 The nuclei tend to have relatively pointed ends when compared with the blunt-ended nuclei in smooth muscle tumours, often with vesicular chromatin. Nuclear palisading reminiscent of that seen in schwannoma may be seen. GISTs with epithelioid morphology account for 20% of cases (Fig. 2(C)). The tumour cells are arranged in sheets or they may have a nested organoid growth pattern, reminiscent of paraganglioma or carcinoid. The tumour cells exhibit eosinophilic or clear cytoplasm (Fig. 2(D)). The cytoplasm may be retracted, simulating cytoplasmic inclusions. The nuclei tend to be round to ovoid and may be pushed to an eccentric location. GISTs of mixed cell type (Fig. 2(E)) may feature an abrupt transition between spindle cell and epithelioid areas or may show an intermediate ovoid cytological appearance. A small minority of GISTs (o5%) have extensive nuclear pleomorphism (Fig. 2(F)). The stroma may be myxoid or it may be hyalinized (Fig. 3(A)) or calcified. Delicate thinwalled blood vessels may be prominent and may be
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Figure 2 Haematoxylin and Eosin sections of GISTs with a spindle cell morphology (A, B), GISTs with an epithelioid morphology (C, D), mixed cell pattern (E) and pleomorphic GIST (F).
associated with stromal haemorrhage (Fig. 3(B)). Necrosis may be present. Lymphocytes can be seen. Small intestinal GISTs may show extracellular bright eosinophilic collagen globules termed ‘skenoid fibres’ (Fig. 3(C)). These structures are periodic acidSchiff (PAS) positive (Fig. 3(D)) and are especially seen in the tumours of the small bowel.
Gastrointestinal autonomic nerve tumours GANTs were originally designated ‘plexoma’ and ‘plexosarcoma’ based on the ultrastructural resem-
blance to cells of autonomic nervous system. GANTs are uncommon tumours that can occasionally develop in the context of von Recklinghausen’s disease19 and Carney’s triad.20 Familial multiple GANTs have been described in an association with intestinal neuronal dysplasia.21 The characteristic ultrastructural features include complex interdigitating cell processes with bulbulous synaptic structures, dense core neurosecretory granules, rudimentary cell junctions and intermediate filaments. Although originally believed to be a distinct tumour, recent evidence supports the concept that GANTs represent a phenotypic variant of GISTs.20
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M. Sabah et al.
Figure 3 GIST with a myxoid stroma (A), stromal haemorrhage (B), skenoid fibres (FC) and PAS-positive skenoid fibres (D).
Immunophenotype The overwhelming majority of GISTs express KIT protein (detected as CD117). The results of KIT immunostaining depend on several technical factors including fixation, tissue preparation, variations in antibody clones in terms of specificity and sensitivity, antibody dilutions and staining techniques. This may account, in part, for the reported immunophenotypic heterogeneity in GISTs. Recently, it has been emphasized that CD117 should be performed without epitope retrieval.22 In our experience and as was previously described,23 the monoclonal antibodies currently available react inconsistently in formalin-fixed paraffin embedded tissue and identify only a minority of GISTs. Given the potential clinical importance of CD117 immunostaining, optimization of the staining techniques and reproducibility are critical. The pattern of staining is variable (Fig. 4). Diffuse strong cytoplasmic staining is the predominant pattern. Membranous staining and dot-like ‘golgi pattern’ staining can be identified. It has been suggested that different staining patterns correlate with different types of c-kit mutations.24 Stromal mast cells and ICC are useful internal positive controls to supplement the normal positive and negative controls.
Immunohistochemical detection of KIT does not necessarily imply c-kit activation. Indeed, CD117 is expressed by other tumour types such as melanoma and soft tissue sarcomas including dermatofibrosarcoma protuberans, synovial sarcoma and angiosarcomas.25 Therefore, CD117 immunoreactivity should be interpreted in the context of morphology and clinical setting. However, it is increasingly recognized that a high level of KIT expression is not characteristic for tumours with non-mutant KIT isoforms or tumours harbouring PDGFRA mutations. CD34 is a transmembrane glycoprotein present on human haematopoietic progenitor cells and vascular endothelium. CD34 is detectable in approximately 70% of GISTs. The oesophageal and rectal GISTs have the highest frequency of CD34 positivity, whereas small intestinal tumours have the lowest percentage of CD34 positivity.26 Actin expression is reported in approximately 30% of cases.26 a-smooth muscle actin (SMA) expression is often reciprocal with CD34 expression: the SMA-positive tumours are often CD34 negative and vice versa. Some tumours may show a mosaic pattern with actin-positive and CD34negative areas and vice versa.26 Desmin-positive immunostaining is uncommon and, if present, is often limited to scattered
ARTICLE IN PRESS Gastrointestinal stromal tumours
405 chemically, the cells are positive for desmin and actin and negative for CD117. Approximately 10–15% of smooth muscle tumours are positive for CD34.24 Pelvic uterine leiomyoma may become attached to the colon and therefore may mimic GIST. These tumours resemble uterine leiomyomas morphologically and are oestrogen and progesterone receptor positive, whereas GISTs are negative for hormonal receptors. Leiomyosarcomas of the GI tract are rare. They are usually associated with nuclear pleomorphism and mitotic activity.
Schwannoma This is a rare mesenchymal tumour in the GI tract. The most common site is the stomach where it appears as a sharply demarcated lesion often surrounded by a lymphoid cuff. The tumour is composed of spindle cells with wavy nuclei. The cells are positive for S100. Antoni B areas may express CD3424; however, the cells are negative for CD117.
Intra-abdominal fibromatosis
Figure 4 Pattern of CD117 immunostaining. GIST showing membranous and cytoplasmic staining (A) and golgi zonelike staining (B).
tumour cells. Prominent staining is more common in epithelioid neoplasms. GISTs are generally negative for S100. Focal positive staining for cytokeratin markers can be seen especially in malignant epithelioid GISTs.
Differential diagnosis The differential diagnosis of GISTs is wide and includes the following.
Smooth muscle tumours True leiomyomas are most common in the oesophagus. Smooth muscle tumours appear less cellular and their cells contain more eosinophilic cytoplasm and cigar-shaped nuclei. Immunohisto-
This is a locally aggressive lesion but usually does not metastasize. It often occurs in the mesentery or reteroperitoneum but may involve the bowel wall. The lesion is composed of spindle cells arranged in parallel bundles with evenly spaced blood vessels. The stroma is usually collagenous with keloid-like fibres. Mitotic figures can be identified. CD117 has been reported to be positive depending on the antibody and technique used.27,28 CD34 is negative.
Inflammatory myofibroblastic tumour This is also known as ‘inflammatory pseudo tumour’. The lesion often occurs in children but may be present in adults. It is usually located on the peritoneal surface, but may involve the omentum, mesentery, stomach or intestinal wall. Whilst some of these lesions are felt to be benign reactions to infectious processes, others have been shown to be clonal in origin.29 Inflammatory myofibroblastic tumours are characterized by spindle cell proliferation admixed with lymphocytes and plasma cells. The cells are positive for desmin and actin and negative for CD117 and CD34. A high proportion of these lesions is also positive for ALK1.29
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Inflammatory fibroid polyp This is a tumour-like lesion that occurs in adults and is most often encountered in the stomach and small intestine. The lesion is usually well circumscribed and is composed of a spindle cell proliferation admixed with granulation tissue-like blood vessels. The cells may show concentric arrangement around the blood vessels—the so-called ‘onion-skin pattern’. Mixed inflammatory cells are usually present, comprising plasma cells, lymphocytes and mast cells. Eosinophils are usually prominent. The majority of these lesions are positive for CD34 but negative for CD117.
Solitary fibrous tumour This lesion may involve the peritoneal cavity and adhere to the bowel. It is characterized by a spindle cell proliferation admixed with collagen. The tumour cells are positive for CD34 but negative for CD117.
Miscellaneous lesions GISTs with epithelioid morphology may be mistaken for paraganglioma, carcinoma or melanoma. Malignant melanoma has a tendency to metastasize to the GI tract. They are CD117 positive but can be distinguished from GISTs by the expression of S100, HMB45 and Melan-A. Dedifferentiated retroperitoneal liposarcoma may be attached to the bowel wall and may sometimes simulate GISTs. Thorough sampling usually reveals a lipomatous component. Angiosarcoma can simulate GIST and can be positive for CD117, but the specific histological and immunohistochemical features allow for the differential diagnosis from GIST.
Prognostic factors Considerable efforts have been made to define variables that may be useful in accurately identifying GISTs with an aggressive clinical behaviour. A series of clincopathological criteria and cytogenetic markers have been implicated in predicting the malignant potential of GISTs.
Clinicopathological factors Tumour stage at presentation The presence of peritoneal or liver metastases at presentation is an adverse prognostic factor and is associated with a shorter survival.30
M. Sabah et al. Tumour size, site and mitotic activity The subset of GISTs that has a high likelihood of malignant behaviour is generally identified by increased tumour size and mitotic activity in the context of tumour location.24,31 The size of the tumour should be measured along the greatest axis of the tumour. The mitotic count is most accurately expressed as the number of mitoses per 50 high power fields (HPFs) and should be performed on areas with the highest mitotic activity. This requires adequate sampling of the tumour. Based on the size of the tumour and the mitotic count, GISTs can be classified into very low risk, low risk, intermediate risk and high risk (Table 1).32 In recent years, it has become clear that GISTs require site evaluation because of differing behaviour.31,33 It has been suggested that the site of the tumour is a prognostic factor independent of the tumour size and mitotic count,33 with small bowel tumours having the worst prognosis. This provided a rationale for the proposed site-specific evaluation of GIST. In this classification, GIST is classified according to the site, size and mitotic count into three categories: benign, malignant and uncertain or low malignant potential (Table 2). Resection margins Incomplete surgical resection is associated with an adverse outcome regardless of all these factors. Epithelioid morphology This cellular pattern is present in one-third of gastric tumours, but is usually associated with more aggressive behaviour when found in the small intestine.
Table 1 Tumour size and mitotic rate as guides to the evaluation of GIST malignancy. GIST categories
Tumour size (cm)
Mitotic count (HPF)
Very low risk
o2
o5/50
Low risk
2–5
o5/50
Intermediate risk
o5 5–10
6–10/50 o5/50
High risk
45 410
45/50 Any mitotic rate 410/50
Any size Adapted from Fletcher et al.32 HPF, high power field.
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Tumour size, mitotic rate and tumour site as guides to the evaluation of GIST malignancy.
GIST categories
Criteria for diagnosis
Probably benign
Intestinal tumours: Maximum diameter p2 cm and no more than 5/50 HPFs Gastric tumours: Maximum diameter p5 cm and no more than 5/50 HPFs
Probably malignant
Intestinal tumours: Maximum diameter 45 cm or more than 5/50 HPFs Gastric tumours: Maximum diameter 410 cm or more than 5/50 HPFs
Uncertain (low malignant potential)
Intestinal tumours: Maximum diameter 42 cm but p5 cm and no more than 5/50 HPFs Gastric tumours: Maximum diameter 45 cm and p10 cm and no more than 5/50 HPFs
Adapted from Miettinen et al.31 HPF, high power field.
Mucosal invasion Mucosal invasion is rarely seen in GISTs but is an adverse prognostic sign34 and is confined to malignant GISTs.31 Mucosal invasion should be distinguished from mucosal ulceration by its diffuse ‘lymphoma-like’ pattern of growth between the glandular elements.31 The presence of mucosal ulceration has no prognostic significance as it is seen in benign and malignant GISTs. Cellularity Low cellularity has emerged as a favourable prognostic feature in some studies.34 Immunohistochemical markers Proliferation markers (Ki-67, MIB-1 and proliferating cell nuclear antigen (PCNA)) may aid in tumour evaluation. It has been reported that tumours with more than 10% of nuclei that are positive for the KI67 analogue are associated with metastases and poor survival rate.35,36 In other studies, the MIB-1 index was not superior to mitotic count as a prognostic factor.37 Alterations of the tumour suppressor gene p16INK4A have been shown to be an independently poor prognostic factor.38 We have previously reported that negative p16 immunostaining is associated with malignant behaviour in GISTs.39
Cytogenetic markers as prognostic factors Prediction of clinical outcome on the basis of morphology alone is not always reliable. Other new and promising parameters that may aid prognostic evaluation may emerge from genetic studies. c-kit and PDGFRA mutations c-kit and PDGFRA mutations are known to be critical steps in initiating primary oncogenic
events. The prognostic value and the therapeutic significance of c-kit mutations remain under investigation. The presence of deletion/insertion mutations involving exon 11 has been identified as an independent negative predictor of disease-free survival.40 In addition, the type of c-kit mutation was found to be of prognostic relevance. KIT exon 11 mutations involving codon 557 and/or 558 were shown to be not only associated with a malignant phenotype, but also with metastatic behaviour.41 Moreover, an association between KIT exon 9 mutations and aggressive behaviour and non-gastric site has been reported.42 Patients with GISTs expressing mutant exon 11 isoforms have a better response to STI-571 compared with patients harbouring mutations in exon 9 or without detectable c-kit mutations.43 Similarly, PDGFRA exon 12 mutations have shown in vivo sensitivity to STI-571 compared with PDGFRA exon 18 mutations.43 Chromosomal losses and gains Certain cytogenetic aberrations have been identified in benign, low malignant potential tumours and malignant GISTs, irrespective of their sites or degree of differentiation, suggesting that these changes are early events in GIST tumourigenesis. These include losses at chromosome arms 14q and 22q. Cytogenetic studies have reported correlations between the acquisition of additional chromosomal changes and aggressive behaviour such as gains at 5p and 20q and losses at chromosomes 1p, 9q and 9p. Gains at 8q and 17q have been detected in metastatic GISTs far more frequently than in primary tumours.44,45 Therefore, these chromosomal aberrations appear to be secondary events and may play an important role in tumour progression (Fig. 5). We have previously investigated loss of heterozygosity (LOH) of the 9p region in malignant and
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M. Sabah et al. double contrast GI X-ray series with barium, endoscopic ultrasound, computed tomography scanning and magnetic resonance. Recently, positron emission tomography scanning has been shown to be a useful and non-invasive means of monitoring the effectiveness of treatment of GISTs.
Treatment options
Telomerase activity Telomerase is an enzyme that extends telomeric repeats on the ends of eukaryotic chromosomes, protecting them from loss, fusion and degradation. Most normal somatic cells do not express telomerase. Telomerase activity has been detected exclusively in malignant GISTs and was absent in benign tumours.46,47 We have examined the expression of hTERT by immunohistochemistry and reported that hTERT expression occurs preferentially in malignant GISTs and that the signal intensity correlated with the mitotic count of the tumour.48
Until recently surgery was the only effective treatment for GISTs and complete surgical resection is still the only treatment that can cure the disease. However, even for patients whose tumour was completely removed with clear margins there is still a high probability of local recurrence. Treatment options for recurrent or metastatic GISTs are even more limited. Radiation therapy is rarely used to treat GISTs because of the radiosensitivity of adjacent organs and the high radioresistance of these tumours. GISTs are highly resistant to conventional chemotherapy, regardless of the agent used. The reasons for this are not fully understood but may relate to the expression of the multi-drug resistance protein products of the MDR1-gene. This bleak prognostic picture for patients with metastatic GISTs has recently changed with the advent of the tyrosine kinase inhibitor (STI-571, Imatinib mesylate, trade names Glivecs in Europe and GleevecTM in the USA; Novartis, Basel, Switzerland). This drug specifically targets c-kit and PDGFRA mutations. It is currently the first-line agent for metastatic GISTs and is under trial to test its possible effect of minimizing the risk of recurrence in patients with high-risk GISTs following complete resection.49 About two-thirds of GIST patients achieve an objective response, defined as 50% or greater tumour volume reduction.50 In addition, another 20% of patients have stabilized disease and as many as 90% of symptomatic patients have relief of symptoms. However, 10% have disease progression despite Imatinib therapy. It is uncertain whether KIT detection is required for treatment eligibility for STI-571, since a subset of GISTs which lack CD117 expression and/or harbour PDGFRA mutations, can also be targeted by STI-571.
Imaging
Ongoing research
Several radiological techniques are used to image primary GISTs and metastatic lesions. These include
The molecular mechanisms of Imatinib resistance and the efficacy of other tyrosine kinase inhibitors
Figure 5 Molecular events involved in the tumourigenesis of GISTs and chromosomal losses and gains involved in the progression of GISTs.
low malignant potential GISTs. We reported that LOH at the 9p region was absent in low malignant potential GISTs but was a common finding in highrisk tumours (malignant and recurrent group). Recurrent GISTs showed more frequent deletions than their primary tumours.39 These findings support the theory that loss of 9p may contribute to the progression and/or malignant transformation of GISTs.
ARTICLE IN PRESS Gastrointestinal stromal tumours are currently under investigation. SU-11248 has shown promising activity in Imatinib-resistant GISTs. In addition to KIT and PDGFRA, this drug also targets FMS-like tyrosine kinase 3 (FLT3) and vascular endothelial nuclear antigen (VEGF) receptors.51
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Practice points
GISTs constitute the largest group of mesenchymal tumours of the GI tract. They originate from the ICC or from stem cells that differentiate towards the ICC KIT has a critical role in clinical practice since the vast majority of GISTs are CD117 positive whereas other mesenchymal tumours of the GI tract are negative CD117-positive immunostaining is not specific for GISTs and should be interpreted in the context of clinical setting and appropriate morphology GISTs with PDGFRA mutations are usually CD117 negative but may respond to STI-571; therefore, KIT detection may not be required for the treatment eligibility for Imatininb Clinically and pathologically, GISTs represent a spectrum of tumours that include benign, malignant and borderline variants Prognostic features indicative of malignancy or high risk for aggressive clinical behaviour are generally identified by increased tumour size and mitotic activity in the context of tumour location Cytogenetic parameters aid prognostic evaluation and may play a role in the prognostication of GISTs in the future
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References 1. Golden T, Stout AP. Smooth muscle tumours of the gastrointestinal tract and retroperitoneal tissues. Surg Gynecol Obstet 1941;73:784–810. 2. Stout AP. Bizarre smooth muscle tumours of the stomach. Cancer 1976;15:400–9. 3. Appelman HD. Cellular leiomyomas of the stomach in 49 patients. Arch Pathol Lab Med 1977;101:373–7. 4. Mazur MT, Clark HB. Gastric stromal tumors. Reappraisal of histogenesis. Am J Surg Pathol 1983;7:507–19. 5. Herrera GA, Pinto dM, Grizzle WE, Han SG. Malignant small bowel neoplasm of enteric plexus derivation (plexosarcoma). Light and electron microscopic study confirming the origin of the neoplasm. Dig Dis Sci 1984;29:275–84. 6. Lauwers GY, Erlandson RA, Casper ES, Brennan MF, Woodruff JM. Gastrointestinal autonomic nerve tumors. A clinico-
21.
22.
23.
24.
25.
pathological, immunohistochemical, and ultrastructural study of 12 cases. Am J Surg Pathol 1993;17:887–97. Miettinen M, Virolainen M, Maarit SR. Gastrointestinal stromal tumors—value of CD34 antigen in their identification and separation from true leiomyomas and schwannomas. Am J Surg Pathol 1995;19:207–16. Hirota S, Isozaki K, Moriyama Y, et al. Gain-of-function mutations of c-kit in human gastrointestinal stromal tumors. Science 1998;279:577–80. Rubin BP, Fletcher JA, Fletcher CD. Molecular Insights into the histogenesis and pathogenesis of gastrointestinal stromal tumors. Int J Surg Pathol 2000;8:5–10. Kindblom LG, Remotti HE, Aldenborg F, Meis-Kindblom JM. Gastrointestinal pacemaker cell tumor (GIPACT): gastrointestinal stromal tumors show phenotypic characteristics of the interstitial cells of Cajal. Am J Pathol 1998;152:1259–69. Miettinen M, Lasota J. Gastrointestinal stromal tumors— definition, clinical, histological, immunohistochemical, and molecular genetic features and differential diagnosis. Virchows Arch 2001;438:1–12. Vliagoftis H, Worobec AS, Metcalfe DD. The protooncogene c-kit and c-kit ligand in human disease. J Allergy Clin Immunol 1997;100:435–40. Isozaki K, Terris B, Belghiti J, Schiffmann S, Hirota S, Vanderwinden JM. Germline-activating mutation in the kinase domain of KIT gene in familial gastrointestinal stromal tumors. Am J Pathol 2000;157:1581–5. Heinrich MC, Rubin BP, Longley BJ, Fletcher JA. Biology and genetic aspects of gastrointestinal stromal tumors: KIT activation and cytogenetic alterations. Hum Pathol 2002; 33:484–95. Debiec-Rychter M, Wasag B, Stul M, et al. Gastrointestinal stromal tumours (GISTs) negative for KIT (CD117 antigen) immunoreactivity. J Pathol 2004;202:430–8. Heinrich MC, Corless CL, Demetri GD, et al. Kinase mutations and imatinib response in patients with metastatic gastrointestinal stromal tumor. J Clin Oncol 2003;21:4342–9. Carney JA. Gastric stromal sarcoma, pulmonary chondroma, and extra-adrenal paraganglioma (Carney triad): natural history, adrenocortical component, and possible familial occurrence. Mayo Clin Proc 1999;74:543–52. Giuly JA, Picand R, Giuly D, Monges B, Nguyen-Cat R. Von Recklinghausen disease and gastrointestinal stromal tumors. Am J Surg 2003;185:86–7. Lespi J, Drut R. [Gastrointestinal autonomic tumor associated with von Recklinghausen’s disease]. Acta Gastroenterol Latinoam 1997;27:271–4. Segal A, Carello S, Caterina P, Papadimitriou JM, Spagnolo DV. Gastrointestinal autonomic nerve tumors: a clinicopathological, immunohistochemical and ultrastructural study of 10 cases. Pathology 1994;26:439–47. O’Brien P, Kapusta L, Dardick I, Axler J, Gnidec A. Multiple familial gastrointestinal autonomic nerve tumors and small intestinal neuronal dysplasia. Am J Surg Pathol 1999;23: 198–204. Fletcher CD, Fletcher JA. Testing for KIT (CD117) in gastrointestinal stromal tumors: another HercepTest? Am J Clin Pathol 2002;118:163–4. Miettinen M, Majidi M, Lasota J. Pathology and diagnostic criteria of gastrointestinal stromal tumors (GISTs): a review. Eur J Cancer 2002;38(Suppl 5):S39–51. Fletcher CD, Berman JJ, Corless C, et al. Diagnosis of gastrointestinal stromal tumors: a consensus approach. Hum Pathol 2002;33:459–65. Sabah M, Leader M, Kay E. The problem with KIT: clinical implications and practical difficulties with CD117
ARTICLE IN PRESS 410
26.
27.
28. 29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
immunostaining. Appl Immunohistochem Mol Morphol 2003;11:56–61. Miettinen M, Sobin LH, Sarlomo-Rikala M. Immunohistochemical spectrum of GISTs at different sites and their differential diagnosis with a reference to CD117 (KIT). Mod Pathol 2000;13:1134–42. Yantiss RK, Spiro IJ, Compton CC, Rosenberg AE. Gastrointestinal stromal tumor versus intra-abdominal fibromatosis of the bowel wall: a clinically important differential diagnosis. Am J Surg Pathol 2000;24:947–57. Miettinen M. Are desmoid tumors kit positive? Am J Surg Pathol 2001;25:549–50. Cook JR, Dehner LP, Collins MH, et al. Anaplastic lymphoma kinase (ALK) expression in the inflammatory myofibroblastic tumor: a comparative immunohistochemical study. Am J Surg Pathol 2001;25:1364–71. Dematteo RP, Lewis JJ, Leung D, Mudan SS, Woodruff JM, Brennan MF. Two hundred gastrointestinal stromal tumors: recurrence patterns and prognostic factors for survival. Ann Surg 2000;231:51–8. Miettinen M, El Rifai W, Sobin HL, Lasota J. Evaluation of malignancy and prognosis of gastrointestinal stromal tumors: a review. Hum Pathol 2002;33:478–83. Fletcher CD, Berman JJ, Corless C, et al. Diagnosis of gastrointestinal stromal tumors: a consensus approach. Int J Surg Pathol 2002;10:81–9. Emory TS, Sobin LH, Lukes L, Lee DH, O’Leary TJ. Prognosis of gastrointestinal smooth-muscle (stromal) tumors: dependence on anatomic site. Am J Surg Pathol 1999;23:82–7. Goldblum JR, Appelman HD. Stromal tumors of the duodenum. A histologic and immunohistochemical study of 20 cases. Am J Surg Pathol 1995;19:71–80. Amin MB, Ma CK, Linden MD, Kubus JJ, Zarbo RJ. Prognostic value of proliferating cell nuclear antigen index in gastric stromal tumors. Correlation with mitotic count and clinical outcome. Am J Clin Pathol 1993;100:428–32. Panizo-Santos A, Sola I, Vega F, et al. Predicting metastatic risk of gastrointestinal stromal tumors: role of cell proliferation and cell cycle regulatory proteins. Int J Surg Pathol 2000;8:133–44. Wong NA, Young R, Malcomson RD, et al. Prognostic indicators for gastrointestinal stromal tumours: a clinicopathological and immunohistochemical study of 108 resected cases of the stomach. Histopathology 2003;43:118–26. Schneider-Stock R, Boltze C, Lasota J, et al. High prognostic value of p16INK4 alterations in gastrointestinal stromal tumors. J Clin Oncol 2003;21:1688–97. Sabah M, Cummins R, Leader M, Kay E. Loss of heterozygosity of chromosome 9p and loss of p16(INK4A) expres-
M. Sabah et al.
40.
41.
42.
43.
44.
45.
46. 47.
48.
49.
50.
51.
sion are associated with malignant gastrointestinal stromal tumors. Mod Pathol 2004;17:1364–71. Singer S, Rubin BP, Lux ML, et al. Prognostic value of KIT mutation type, mitotic activity, and histologic subtype in gastrointestinal stromal tumors. J Clin Oncol 2002;20: 3898–905. Wardelmann E, Losen I, Hans V, et al. Deletion of Trp-557 and Lys-558 in the juxtamembrane domain of the c-kit protooncogene is associated with metastatic behavior of gastrointestinal stromal tumors. Int J Cancer 2003;106: 887–95. Antonescu CR, Sommer G, Sarran L, et al. Association of KIT exon 9 mutations with nongastric primary site and aggressive behavior: KIT mutation analysis and clinical correlates of 120 gastrointestinal stromal tumors. Clin Cancer Res 2003;9:3329–37. Debiec-Rychter M, Dumez H, Judson I, et al. Use of c-KIT/ PDGFRA mutational analysis to predict the clinical response to imatinib in patients with advanced gastrointestinal stromal tumours entered on phase I and II studies of the EORTC Soft Tissue and Bone Sarcoma Group. Eur J Cancer 2004;40:689–95. Debiec-Rychter M, Lasota J, Sarlomo-Rikala M, Kordek R, Miettinen M. Chromosomal aberrations in malignant gastrointestinal stromal tumors: correlation with c-KIT gene mutation. Cancer Genet Cytogenet 2001;128:24–30. Kim NG, Kim JJ, Ahn JY, et al. Putative chromosomal deletions on 9P, 9Q and 22Q occur preferentially in malignant gastrointestinal stromal tumors. Int J Cancer 2000;85:633–8. Sakurai S, Fukayama M, Kaizaki Y, et al. Telomerase activity in gastrointestinal stromal tumors. Cancer 1998;83:2060–6. Gunther T, Schneider-Stock R, Hackel C, et al. Telomerase activity and expression of hTRT and hTR in gastrointestinal stromal tumors in comparison with extragastrointestinal sarcomas. Clin Cancer Res 2000;6:1811–8. Sabah M, Cummins R, Leader M, Kay E. Expression of human telomerase reverse transcriptase in gastrointestinal stromal tumors occurs preferentially in malignant neoplasms. Hum Pathol 2004;35:1231–5. Dematteo RP, Heinrich MC, El Rifai WM, Demetri G. Clinical management of gastrointestinal stromal tumors: before and after STI-571. Hum Pathol 2002;33:466–77. van Oosterom AT, Judson I, Verweij J, et al. Safety and efficacy of imatinib (STI571) in metastatic gastrointestinal stromal tumours: a phase I study. Lancet 2001;358: 1421–3. Sakamoto KM. Su-11248 Sugen. Curr Opin Investig Drugs 2004;5(12):1329–39.
www.elsevier.com/locate/cdip
MINI-SYMPOSIUM: BONE AND SOFT TISSUE PATHOLOGY
Gastrointestinal stromal tumours: An update Muna Sabah, Mary Leader, Elaine Kay Department of Histopathology, Education and Research Centre, Beaumont Hospital and Royal College of Surgeons in Ireland, Dublin 9, Ireland
KEYWORDS GIST; KIT; Morphology; Prognosis
Summary Gastrointestinal stromal tumours (GISTs) comprise the largest subset of mesenchymal tumours of the digestive tract. These tumours have been the subject of considerable debate in the literature regarding their histogenesis, criteria for diagnosis, prognostic features and biological behaviour. The majority of GISTs express CD117 immunostaining and show various degrees of differentiation towards the phenotype of interstitial cell of Cajal. Clinically and histologically, GISTs represent a spectrum that includes benign and malignant variants. The prediction of clinical behaviour is best achieved by evaluation of multiple parameters including clinical, morphological and cytogenetic features. The recognition of the central role played by activating mutations of c-kit and platelet derived growth factor receptor alpha in the pathogenesis of GISTs and the introduction of STI-571, a receptor tyrosine kinase inhibitor that has proved extremely effective in the treatment of GISTs, have not only have focused attention on these tumours but also made it necessary to accurately define these tumours and separate them from other mesenchymal lesions. This review discusses the definition, histogenesis, epidemiology, clinical presentation, morphological and immunohistochemical features and the differential diagnosis of GISTs and addresses predictors of malignancy and management of GISTs. & 2005 Elsevier Ltd. All rights reserved.
Historical overview: from Stout to molecular revolution The first accurate description of mesenchymal neoplasms of the gastrointestinal (GI) tract was in 1941.1 Traditionally, these tumours were thought to Corresponding author. Tel.: +353 1 809 2541;
fax: +353 1 809 3720. E-mail address: [email protected] (M. Sabah).
be derived from smooth muscle cells, based on their resemblance to smooth muscle tumours and they were designated as leiomyomas, bizarre leiomyomas,2 cellular leiomyomas3 and leiomyosarcomas. However, with the advent of electron microscopy, it has been shown that relatively few neoplasms showed convincing ultrastructural evidence of smooth muscle differentiation. The application of immunohistochemistry revealed that many of these neoplasms lacked the immunophenotypical features
0968-6053/$ - see front matter & 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.cdip.2005.08.003
ARTICLE IN PRESS Gastrointestinal stromal tumours of smooth muscle differentiation. This led Mazur and Clark4 in 1983 to introduce the generic designation ‘stromal tumour’. Subsequently, Herrera et al.5 introduced the concept of ‘plexosarcoma’ in 1984 to acknowledge the existence of a small subset of stromal tumours with autonomic neuronal differentiation which became better known as gastrointestinal autonomic nerve tumours (GANTs).6 There was considerable controversy as to the line of differentiation, since some tumours exhibited a myogenic phenotype, others showed neural differentiation, some revealed mixed differentiation and some cases did not show any specific line of differentiation, the ‘null phenotype’. Some enthusiasm was generated by the recognition that a significant proportion of stromal tumours express CD34.7 However, the diagnostic utility of this marker was hampered by its poor specificity. As a consequence of the lack of reproducible diagnostic criteria, gastrointestinal stromal tumour (GIST) represented a generic term to indicate any mesenchymal tumour arising in the GI tract. The recognition of the central role of c-kit mutations in the pathogenesis of GISTs8,9 and, in most cases, the associated expression of KIT protein in these tumours has provided a reproducible genotypic and phenotypic marker.10 Therefore, KIT (CD117 in the standardized terminology of leucocyte antigens) expression has emerged as a marker for discriminating GISTs from other mesenchymal GI neoplasms and some have equated immunoreactivity for KIT as the definition of GISTs.11 Recently, it has become apparent that some GISTs that lacked c-kit mutations were found to have activating mutations of platelet derived growth factor receptor (PDGFRA). Therefore, the definition of GISTs may need to be revised. GISTs may now be considered to encompass mesenchymal tumours that express KIT protein or have activating mutations of receptor tyrosine kinase genes (c-kit or platelet derived growth factor receptor alpha (PDGFRA)). However, for most clinical purposes, GISTs may simply be referred to as KIT-positive tumours with appropriate morphology, although this definition is somewhat inaccurate.
401 smooth muscle cells. Their principal function is to generate autonomous rhythmic contractions, involved in digestion and peristalsis. Therefore, these cells are known as GI ‘pacemaker’ cells. Immunohistochemical studies revealed that GISTs have similar features to ICC, being positive with CD34 and CD117 and negative or variably positive for other neural and smooth muscle markers.10
Molecular biology (c-kit and PDGFRA mutations) The c-kit proto-oncogene, located on the long arm of chromosome 4, encodes a class III transmembrane tyrosine kinase receptor.12 KIT protein consists of an extracellular ligand-binding site and an intracellular kinase domain. The ligand for KIT is a growth factor called the stem cell factor. Extracellular binding of stem cell factor results in dimerization of the receptor, triggering phosphorylation of the kinase domain. This induces a signalling cascade that propagates through the cytoplasm into the nucleus. This signalling cascade affects many aspects of cellular behaviour including proliferation, differentiation, adhesion and apoptosis.12 KIT expression is extremely important in the development of several cell types including haematopoietic stem cells, mast cells, germ cells, melanocytes, some epithelial cells and the ICC.12 Gains of function mutations of c-kit have been observed in sporadic GISTs and, less commonly, as germline mutations in familial GISTs,8,13 suggesting that constitutive expression of KIT plays a significant role in the tumourigenesis of GISTs. The most common mutations are in the juxtamembrane
Histogenesis It has been suggested that GISTs originate from the interstitial cell of Cajal (ICC), or from a primitive stem cell that differentiates towards both the ICC and smooth muscle phenotye.9,10 The ICCs are intercalated between the autonomic nerves and
Figure 1 c-kit mutations in the juxtamembrane cellular domain of exon 11 are seen in 71% of GISTs. Mutations in the extracellular domain of exon 9 and mutations in the tyrosine kinase domain on exons 13 and 17 are less common. Modified from Heinrich et al.14
ARTICLE IN PRESS 402 region in exon 11, resulting in ligand-independent activation of the tyrosine kinase activity.8 Mutations in exon 9 (extracellular domain) and rarely in exon 13 (kinase domain) or 17 (the phosphotransferase domain) can be detected (Fig. 1).14 However, around 10–15% of GISTs lack KIT expression.15 Within this group a large subset would have gain of function mutations of PDGFRA.16 Mutations in PDGFRA provide an alternative mechanism in GIST oncogenesis.
Epidemiology and risk factors The lack of accepted diagnostic criteria for GISTs has led to variation in the current estimate of disease incidence. GIST is a relatively rare neoplasm representing less than 1% of all primary tumours of the GI tract with an incidence of approximately 10–20/million.11 Disease incidence appears to be uniform across all geographical and ethnic populations. GISTs predominantly arise in the middle aged or elderly and are rare in young adults. The median age is around 60 years. There is no gender preference except in the setting of Carney17 triad (malignant gastric epithelioid stromal tumour, pulmonary chondroma and functioning extra-adrenal paraganglioma), nearly all of which occur in females. There are no known risk factors; however, genetic influence has been described, including reports of familial GISTs13 and GISTs in association with von Recklinghausen’s disease.18
Clinical presentation GISTs present a spectrum from clinically benign tumours to sarcomas. The symptoms vary according to the size and location of the tumour. Small tumours are asymptomatic and found incidentally at laparotomy, endoscopy or during radiological studies for other conditions. Symptomatic tumours often present with abdominal discomfort. They may ulcerate and present with GI bleeding. Lesions in the oesophagus may present with dysphagia, while intestinal neoplasms may present with abdominal mass, obstruction or perforation. Some patients present with metastases, particularly to the liver. GISTs occur at every level of the GI tract. Most tumours arise in the stomach (60%) and about 20–30% occur in the small intestine. Colorectal and oesophageal GISTs account for less than 10%.11 A small proportion of GISTs arise in extra-GI tract sites including the omentum, mesentery and retroperitoneum.
M. Sabah et al.
Morphology Gross features GISTs range in size from several millimetres to over 30 cm. Most lesions are well circumscribed, but unencapsulated. Some are multi-nodular. They may have a whorled fibroid-like cut surface or they may be fleshy in appearance. Areas of haemorrhage, cystic degeneration and central necrosis may be seen. GISTs tend to be primarily intramural tumours, usually involving the submucosa and muscularis propria. Large tumours may have a dumbbell appearance with the tumour protruding both into the lumen and from the serosa.
Microscopic features GISTs show a spectrum of histological features. Morphologically, the cells of GISTs are spindle, epithelioid, mixed pattern and occasionally pleomorphic. Spindle cell type is the predominant pattern, seen in 70% of GIST cases (Fig. 2(A)). The tumour cells are arranged in short fascicles, whorls or a storiform growth pattern. The neoplastic cells have light fibrillary eosinophilic cytoplasm with indistinct cell borders. Perinuclear vacuoles are present and indent the nucleus at one pole (Fig. 2(B)). These vacuoles are an artefact of fixation since they are not present in frozen sections.3 The nuclei tend to have relatively pointed ends when compared with the blunt-ended nuclei in smooth muscle tumours, often with vesicular chromatin. Nuclear palisading reminiscent of that seen in schwannoma may be seen. GISTs with epithelioid morphology account for 20% of cases (Fig. 2(C)). The tumour cells are arranged in sheets or they may have a nested organoid growth pattern, reminiscent of paraganglioma or carcinoid. The tumour cells exhibit eosinophilic or clear cytoplasm (Fig. 2(D)). The cytoplasm may be retracted, simulating cytoplasmic inclusions. The nuclei tend to be round to ovoid and may be pushed to an eccentric location. GISTs of mixed cell type (Fig. 2(E)) may feature an abrupt transition between spindle cell and epithelioid areas or may show an intermediate ovoid cytological appearance. A small minority of GISTs (o5%) have extensive nuclear pleomorphism (Fig. 2(F)). The stroma may be myxoid or it may be hyalinized (Fig. 3(A)) or calcified. Delicate thinwalled blood vessels may be prominent and may be
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Figure 2 Haematoxylin and Eosin sections of GISTs with a spindle cell morphology (A, B), GISTs with an epithelioid morphology (C, D), mixed cell pattern (E) and pleomorphic GIST (F).
associated with stromal haemorrhage (Fig. 3(B)). Necrosis may be present. Lymphocytes can be seen. Small intestinal GISTs may show extracellular bright eosinophilic collagen globules termed ‘skenoid fibres’ (Fig. 3(C)). These structures are periodic acidSchiff (PAS) positive (Fig. 3(D)) and are especially seen in the tumours of the small bowel.
Gastrointestinal autonomic nerve tumours GANTs were originally designated ‘plexoma’ and ‘plexosarcoma’ based on the ultrastructural resem-
blance to cells of autonomic nervous system. GANTs are uncommon tumours that can occasionally develop in the context of von Recklinghausen’s disease19 and Carney’s triad.20 Familial multiple GANTs have been described in an association with intestinal neuronal dysplasia.21 The characteristic ultrastructural features include complex interdigitating cell processes with bulbulous synaptic structures, dense core neurosecretory granules, rudimentary cell junctions and intermediate filaments. Although originally believed to be a distinct tumour, recent evidence supports the concept that GANTs represent a phenotypic variant of GISTs.20
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Figure 3 GIST with a myxoid stroma (A), stromal haemorrhage (B), skenoid fibres (FC) and PAS-positive skenoid fibres (D).
Immunophenotype The overwhelming majority of GISTs express KIT protein (detected as CD117). The results of KIT immunostaining depend on several technical factors including fixation, tissue preparation, variations in antibody clones in terms of specificity and sensitivity, antibody dilutions and staining techniques. This may account, in part, for the reported immunophenotypic heterogeneity in GISTs. Recently, it has been emphasized that CD117 should be performed without epitope retrieval.22 In our experience and as was previously described,23 the monoclonal antibodies currently available react inconsistently in formalin-fixed paraffin embedded tissue and identify only a minority of GISTs. Given the potential clinical importance of CD117 immunostaining, optimization of the staining techniques and reproducibility are critical. The pattern of staining is variable (Fig. 4). Diffuse strong cytoplasmic staining is the predominant pattern. Membranous staining and dot-like ‘golgi pattern’ staining can be identified. It has been suggested that different staining patterns correlate with different types of c-kit mutations.24 Stromal mast cells and ICC are useful internal positive controls to supplement the normal positive and negative controls.
Immunohistochemical detection of KIT does not necessarily imply c-kit activation. Indeed, CD117 is expressed by other tumour types such as melanoma and soft tissue sarcomas including dermatofibrosarcoma protuberans, synovial sarcoma and angiosarcomas.25 Therefore, CD117 immunoreactivity should be interpreted in the context of morphology and clinical setting. However, it is increasingly recognized that a high level of KIT expression is not characteristic for tumours with non-mutant KIT isoforms or tumours harbouring PDGFRA mutations. CD34 is a transmembrane glycoprotein present on human haematopoietic progenitor cells and vascular endothelium. CD34 is detectable in approximately 70% of GISTs. The oesophageal and rectal GISTs have the highest frequency of CD34 positivity, whereas small intestinal tumours have the lowest percentage of CD34 positivity.26 Actin expression is reported in approximately 30% of cases.26 a-smooth muscle actin (SMA) expression is often reciprocal with CD34 expression: the SMA-positive tumours are often CD34 negative and vice versa. Some tumours may show a mosaic pattern with actin-positive and CD34negative areas and vice versa.26 Desmin-positive immunostaining is uncommon and, if present, is often limited to scattered
ARTICLE IN PRESS Gastrointestinal stromal tumours
405 chemically, the cells are positive for desmin and actin and negative for CD117. Approximately 10–15% of smooth muscle tumours are positive for CD34.24 Pelvic uterine leiomyoma may become attached to the colon and therefore may mimic GIST. These tumours resemble uterine leiomyomas morphologically and are oestrogen and progesterone receptor positive, whereas GISTs are negative for hormonal receptors. Leiomyosarcomas of the GI tract are rare. They are usually associated with nuclear pleomorphism and mitotic activity.
Schwannoma This is a rare mesenchymal tumour in the GI tract. The most common site is the stomach where it appears as a sharply demarcated lesion often surrounded by a lymphoid cuff. The tumour is composed of spindle cells with wavy nuclei. The cells are positive for S100. Antoni B areas may express CD3424; however, the cells are negative for CD117.
Intra-abdominal fibromatosis
Figure 4 Pattern of CD117 immunostaining. GIST showing membranous and cytoplasmic staining (A) and golgi zonelike staining (B).
tumour cells. Prominent staining is more common in epithelioid neoplasms. GISTs are generally negative for S100. Focal positive staining for cytokeratin markers can be seen especially in malignant epithelioid GISTs.
Differential diagnosis The differential diagnosis of GISTs is wide and includes the following.
Smooth muscle tumours True leiomyomas are most common in the oesophagus. Smooth muscle tumours appear less cellular and their cells contain more eosinophilic cytoplasm and cigar-shaped nuclei. Immunohisto-
This is a locally aggressive lesion but usually does not metastasize. It often occurs in the mesentery or reteroperitoneum but may involve the bowel wall. The lesion is composed of spindle cells arranged in parallel bundles with evenly spaced blood vessels. The stroma is usually collagenous with keloid-like fibres. Mitotic figures can be identified. CD117 has been reported to be positive depending on the antibody and technique used.27,28 CD34 is negative.
Inflammatory myofibroblastic tumour This is also known as ‘inflammatory pseudo tumour’. The lesion often occurs in children but may be present in adults. It is usually located on the peritoneal surface, but may involve the omentum, mesentery, stomach or intestinal wall. Whilst some of these lesions are felt to be benign reactions to infectious processes, others have been shown to be clonal in origin.29 Inflammatory myofibroblastic tumours are characterized by spindle cell proliferation admixed with lymphocytes and plasma cells. The cells are positive for desmin and actin and negative for CD117 and CD34. A high proportion of these lesions is also positive for ALK1.29
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Inflammatory fibroid polyp This is a tumour-like lesion that occurs in adults and is most often encountered in the stomach and small intestine. The lesion is usually well circumscribed and is composed of a spindle cell proliferation admixed with granulation tissue-like blood vessels. The cells may show concentric arrangement around the blood vessels—the so-called ‘onion-skin pattern’. Mixed inflammatory cells are usually present, comprising plasma cells, lymphocytes and mast cells. Eosinophils are usually prominent. The majority of these lesions are positive for CD34 but negative for CD117.
Solitary fibrous tumour This lesion may involve the peritoneal cavity and adhere to the bowel. It is characterized by a spindle cell proliferation admixed with collagen. The tumour cells are positive for CD34 but negative for CD117.
Miscellaneous lesions GISTs with epithelioid morphology may be mistaken for paraganglioma, carcinoma or melanoma. Malignant melanoma has a tendency to metastasize to the GI tract. They are CD117 positive but can be distinguished from GISTs by the expression of S100, HMB45 and Melan-A. Dedifferentiated retroperitoneal liposarcoma may be attached to the bowel wall and may sometimes simulate GISTs. Thorough sampling usually reveals a lipomatous component. Angiosarcoma can simulate GIST and can be positive for CD117, but the specific histological and immunohistochemical features allow for the differential diagnosis from GIST.
Prognostic factors Considerable efforts have been made to define variables that may be useful in accurately identifying GISTs with an aggressive clinical behaviour. A series of clincopathological criteria and cytogenetic markers have been implicated in predicting the malignant potential of GISTs.
Clinicopathological factors Tumour stage at presentation The presence of peritoneal or liver metastases at presentation is an adverse prognostic factor and is associated with a shorter survival.30
M. Sabah et al. Tumour size, site and mitotic activity The subset of GISTs that has a high likelihood of malignant behaviour is generally identified by increased tumour size and mitotic activity in the context of tumour location.24,31 The size of the tumour should be measured along the greatest axis of the tumour. The mitotic count is most accurately expressed as the number of mitoses per 50 high power fields (HPFs) and should be performed on areas with the highest mitotic activity. This requires adequate sampling of the tumour. Based on the size of the tumour and the mitotic count, GISTs can be classified into very low risk, low risk, intermediate risk and high risk (Table 1).32 In recent years, it has become clear that GISTs require site evaluation because of differing behaviour.31,33 It has been suggested that the site of the tumour is a prognostic factor independent of the tumour size and mitotic count,33 with small bowel tumours having the worst prognosis. This provided a rationale for the proposed site-specific evaluation of GIST. In this classification, GIST is classified according to the site, size and mitotic count into three categories: benign, malignant and uncertain or low malignant potential (Table 2). Resection margins Incomplete surgical resection is associated with an adverse outcome regardless of all these factors. Epithelioid morphology This cellular pattern is present in one-third of gastric tumours, but is usually associated with more aggressive behaviour when found in the small intestine.
Table 1 Tumour size and mitotic rate as guides to the evaluation of GIST malignancy. GIST categories
Tumour size (cm)
Mitotic count (HPF)
Very low risk
o2
o5/50
Low risk
2–5
o5/50
Intermediate risk
o5 5–10
6–10/50 o5/50
High risk
45 410
45/50 Any mitotic rate 410/50
Any size Adapted from Fletcher et al.32 HPF, high power field.
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Tumour size, mitotic rate and tumour site as guides to the evaluation of GIST malignancy.
GIST categories
Criteria for diagnosis
Probably benign
Intestinal tumours: Maximum diameter p2 cm and no more than 5/50 HPFs Gastric tumours: Maximum diameter p5 cm and no more than 5/50 HPFs
Probably malignant
Intestinal tumours: Maximum diameter 45 cm or more than 5/50 HPFs Gastric tumours: Maximum diameter 410 cm or more than 5/50 HPFs
Uncertain (low malignant potential)
Intestinal tumours: Maximum diameter 42 cm but p5 cm and no more than 5/50 HPFs Gastric tumours: Maximum diameter 45 cm and p10 cm and no more than 5/50 HPFs
Adapted from Miettinen et al.31 HPF, high power field.
Mucosal invasion Mucosal invasion is rarely seen in GISTs but is an adverse prognostic sign34 and is confined to malignant GISTs.31 Mucosal invasion should be distinguished from mucosal ulceration by its diffuse ‘lymphoma-like’ pattern of growth between the glandular elements.31 The presence of mucosal ulceration has no prognostic significance as it is seen in benign and malignant GISTs. Cellularity Low cellularity has emerged as a favourable prognostic feature in some studies.34 Immunohistochemical markers Proliferation markers (Ki-67, MIB-1 and proliferating cell nuclear antigen (PCNA)) may aid in tumour evaluation. It has been reported that tumours with more than 10% of nuclei that are positive for the KI67 analogue are associated with metastases and poor survival rate.35,36 In other studies, the MIB-1 index was not superior to mitotic count as a prognostic factor.37 Alterations of the tumour suppressor gene p16INK4A have been shown to be an independently poor prognostic factor.38 We have previously reported that negative p16 immunostaining is associated with malignant behaviour in GISTs.39
Cytogenetic markers as prognostic factors Prediction of clinical outcome on the basis of morphology alone is not always reliable. Other new and promising parameters that may aid prognostic evaluation may emerge from genetic studies. c-kit and PDGFRA mutations c-kit and PDGFRA mutations are known to be critical steps in initiating primary oncogenic
events. The prognostic value and the therapeutic significance of c-kit mutations remain under investigation. The presence of deletion/insertion mutations involving exon 11 has been identified as an independent negative predictor of disease-free survival.40 In addition, the type of c-kit mutation was found to be of prognostic relevance. KIT exon 11 mutations involving codon 557 and/or 558 were shown to be not only associated with a malignant phenotype, but also with metastatic behaviour.41 Moreover, an association between KIT exon 9 mutations and aggressive behaviour and non-gastric site has been reported.42 Patients with GISTs expressing mutant exon 11 isoforms have a better response to STI-571 compared with patients harbouring mutations in exon 9 or without detectable c-kit mutations.43 Similarly, PDGFRA exon 12 mutations have shown in vivo sensitivity to STI-571 compared with PDGFRA exon 18 mutations.43 Chromosomal losses and gains Certain cytogenetic aberrations have been identified in benign, low malignant potential tumours and malignant GISTs, irrespective of their sites or degree of differentiation, suggesting that these changes are early events in GIST tumourigenesis. These include losses at chromosome arms 14q and 22q. Cytogenetic studies have reported correlations between the acquisition of additional chromosomal changes and aggressive behaviour such as gains at 5p and 20q and losses at chromosomes 1p, 9q and 9p. Gains at 8q and 17q have been detected in metastatic GISTs far more frequently than in primary tumours.44,45 Therefore, these chromosomal aberrations appear to be secondary events and may play an important role in tumour progression (Fig. 5). We have previously investigated loss of heterozygosity (LOH) of the 9p region in malignant and
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M. Sabah et al. double contrast GI X-ray series with barium, endoscopic ultrasound, computed tomography scanning and magnetic resonance. Recently, positron emission tomography scanning has been shown to be a useful and non-invasive means of monitoring the effectiveness of treatment of GISTs.
Treatment options
Telomerase activity Telomerase is an enzyme that extends telomeric repeats on the ends of eukaryotic chromosomes, protecting them from loss, fusion and degradation. Most normal somatic cells do not express telomerase. Telomerase activity has been detected exclusively in malignant GISTs and was absent in benign tumours.46,47 We have examined the expression of hTERT by immunohistochemistry and reported that hTERT expression occurs preferentially in malignant GISTs and that the signal intensity correlated with the mitotic count of the tumour.48
Until recently surgery was the only effective treatment for GISTs and complete surgical resection is still the only treatment that can cure the disease. However, even for patients whose tumour was completely removed with clear margins there is still a high probability of local recurrence. Treatment options for recurrent or metastatic GISTs are even more limited. Radiation therapy is rarely used to treat GISTs because of the radiosensitivity of adjacent organs and the high radioresistance of these tumours. GISTs are highly resistant to conventional chemotherapy, regardless of the agent used. The reasons for this are not fully understood but may relate to the expression of the multi-drug resistance protein products of the MDR1-gene. This bleak prognostic picture for patients with metastatic GISTs has recently changed with the advent of the tyrosine kinase inhibitor (STI-571, Imatinib mesylate, trade names Glivecs in Europe and GleevecTM in the USA; Novartis, Basel, Switzerland). This drug specifically targets c-kit and PDGFRA mutations. It is currently the first-line agent for metastatic GISTs and is under trial to test its possible effect of minimizing the risk of recurrence in patients with high-risk GISTs following complete resection.49 About two-thirds of GIST patients achieve an objective response, defined as 50% or greater tumour volume reduction.50 In addition, another 20% of patients have stabilized disease and as many as 90% of symptomatic patients have relief of symptoms. However, 10% have disease progression despite Imatinib therapy. It is uncertain whether KIT detection is required for treatment eligibility for STI-571, since a subset of GISTs which lack CD117 expression and/or harbour PDGFRA mutations, can also be targeted by STI-571.
Imaging
Ongoing research
Several radiological techniques are used to image primary GISTs and metastatic lesions. These include
The molecular mechanisms of Imatinib resistance and the efficacy of other tyrosine kinase inhibitors
Figure 5 Molecular events involved in the tumourigenesis of GISTs and chromosomal losses and gains involved in the progression of GISTs.
low malignant potential GISTs. We reported that LOH at the 9p region was absent in low malignant potential GISTs but was a common finding in highrisk tumours (malignant and recurrent group). Recurrent GISTs showed more frequent deletions than their primary tumours.39 These findings support the theory that loss of 9p may contribute to the progression and/or malignant transformation of GISTs.
ARTICLE IN PRESS Gastrointestinal stromal tumours are currently under investigation. SU-11248 has shown promising activity in Imatinib-resistant GISTs. In addition to KIT and PDGFRA, this drug also targets FMS-like tyrosine kinase 3 (FLT3) and vascular endothelial nuclear antigen (VEGF) receptors.51
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Practice points
GISTs constitute the largest group of mesenchymal tumours of the GI tract. They originate from the ICC or from stem cells that differentiate towards the ICC KIT has a critical role in clinical practice since the vast majority of GISTs are CD117 positive whereas other mesenchymal tumours of the GI tract are negative CD117-positive immunostaining is not specific for GISTs and should be interpreted in the context of clinical setting and appropriate morphology GISTs with PDGFRA mutations are usually CD117 negative but may respond to STI-571; therefore, KIT detection may not be required for the treatment eligibility for Imatininb Clinically and pathologically, GISTs represent a spectrum of tumours that include benign, malignant and borderline variants Prognostic features indicative of malignancy or high risk for aggressive clinical behaviour are generally identified by increased tumour size and mitotic activity in the context of tumour location Cytogenetic parameters aid prognostic evaluation and may play a role in the prognostication of GISTs in the future
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References 1. Golden T, Stout AP. Smooth muscle tumours of the gastrointestinal tract and retroperitoneal tissues. Surg Gynecol Obstet 1941;73:784–810. 2. Stout AP. Bizarre smooth muscle tumours of the stomach. Cancer 1976;15:400–9. 3. Appelman HD. Cellular leiomyomas of the stomach in 49 patients. Arch Pathol Lab Med 1977;101:373–7. 4. Mazur MT, Clark HB. Gastric stromal tumors. Reappraisal of histogenesis. Am J Surg Pathol 1983;7:507–19. 5. Herrera GA, Pinto dM, Grizzle WE, Han SG. Malignant small bowel neoplasm of enteric plexus derivation (plexosarcoma). Light and electron microscopic study confirming the origin of the neoplasm. Dig Dis Sci 1984;29:275–84. 6. Lauwers GY, Erlandson RA, Casper ES, Brennan MF, Woodruff JM. Gastrointestinal autonomic nerve tumors. A clinico-
21.
22.
23.
24.
25.
pathological, immunohistochemical, and ultrastructural study of 12 cases. Am J Surg Pathol 1993;17:887–97. Miettinen M, Virolainen M, Maarit SR. Gastrointestinal stromal tumors—value of CD34 antigen in their identification and separation from true leiomyomas and schwannomas. Am J Surg Pathol 1995;19:207–16. Hirota S, Isozaki K, Moriyama Y, et al. Gain-of-function mutations of c-kit in human gastrointestinal stromal tumors. Science 1998;279:577–80. Rubin BP, Fletcher JA, Fletcher CD. Molecular Insights into the histogenesis and pathogenesis of gastrointestinal stromal tumors. Int J Surg Pathol 2000;8:5–10. Kindblom LG, Remotti HE, Aldenborg F, Meis-Kindblom JM. Gastrointestinal pacemaker cell tumor (GIPACT): gastrointestinal stromal tumors show phenotypic characteristics of the interstitial cells of Cajal. Am J Pathol 1998;152:1259–69. Miettinen M, Lasota J. Gastrointestinal stromal tumors— definition, clinical, histological, immunohistochemical, and molecular genetic features and differential diagnosis. Virchows Arch 2001;438:1–12. Vliagoftis H, Worobec AS, Metcalfe DD. The protooncogene c-kit and c-kit ligand in human disease. J Allergy Clin Immunol 1997;100:435–40. Isozaki K, Terris B, Belghiti J, Schiffmann S, Hirota S, Vanderwinden JM. Germline-activating mutation in the kinase domain of KIT gene in familial gastrointestinal stromal tumors. Am J Pathol 2000;157:1581–5. Heinrich MC, Rubin BP, Longley BJ, Fletcher JA. Biology and genetic aspects of gastrointestinal stromal tumors: KIT activation and cytogenetic alterations. Hum Pathol 2002; 33:484–95. Debiec-Rychter M, Wasag B, Stul M, et al. Gastrointestinal stromal tumours (GISTs) negative for KIT (CD117 antigen) immunoreactivity. J Pathol 2004;202:430–8. Heinrich MC, Corless CL, Demetri GD, et al. Kinase mutations and imatinib response in patients with metastatic gastrointestinal stromal tumor. J Clin Oncol 2003;21:4342–9. Carney JA. Gastric stromal sarcoma, pulmonary chondroma, and extra-adrenal paraganglioma (Carney triad): natural history, adrenocortical component, and possible familial occurrence. Mayo Clin Proc 1999;74:543–52. Giuly JA, Picand R, Giuly D, Monges B, Nguyen-Cat R. Von Recklinghausen disease and gastrointestinal stromal tumors. Am J Surg 2003;185:86–7. Lespi J, Drut R. [Gastrointestinal autonomic tumor associated with von Recklinghausen’s disease]. Acta Gastroenterol Latinoam 1997;27:271–4. Segal A, Carello S, Caterina P, Papadimitriou JM, Spagnolo DV. Gastrointestinal autonomic nerve tumors: a clinicopathological, immunohistochemical and ultrastructural study of 10 cases. Pathology 1994;26:439–47. O’Brien P, Kapusta L, Dardick I, Axler J, Gnidec A. Multiple familial gastrointestinal autonomic nerve tumors and small intestinal neuronal dysplasia. Am J Surg Pathol 1999;23: 198–204. Fletcher CD, Fletcher JA. Testing for KIT (CD117) in gastrointestinal stromal tumors: another HercepTest? Am J Clin Pathol 2002;118:163–4. Miettinen M, Majidi M, Lasota J. Pathology and diagnostic criteria of gastrointestinal stromal tumors (GISTs): a review. Eur J Cancer 2002;38(Suppl 5):S39–51. Fletcher CD, Berman JJ, Corless C, et al. Diagnosis of gastrointestinal stromal tumors: a consensus approach. Hum Pathol 2002;33:459–65. Sabah M, Leader M, Kay E. The problem with KIT: clinical implications and practical difficulties with CD117
ARTICLE IN PRESS 410
26.
27.
28. 29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
immunostaining. Appl Immunohistochem Mol Morphol 2003;11:56–61. Miettinen M, Sobin LH, Sarlomo-Rikala M. Immunohistochemical spectrum of GISTs at different sites and their differential diagnosis with a reference to CD117 (KIT). Mod Pathol 2000;13:1134–42. Yantiss RK, Spiro IJ, Compton CC, Rosenberg AE. Gastrointestinal stromal tumor versus intra-abdominal fibromatosis of the bowel wall: a clinically important differential diagnosis. Am J Surg Pathol 2000;24:947–57. Miettinen M. Are desmoid tumors kit positive? Am J Surg Pathol 2001;25:549–50. Cook JR, Dehner LP, Collins MH, et al. Anaplastic lymphoma kinase (ALK) expression in the inflammatory myofibroblastic tumor: a comparative immunohistochemical study. Am J Surg Pathol 2001;25:1364–71. Dematteo RP, Lewis JJ, Leung D, Mudan SS, Woodruff JM, Brennan MF. Two hundred gastrointestinal stromal tumors: recurrence patterns and prognostic factors for survival. Ann Surg 2000;231:51–8. Miettinen M, El Rifai W, Sobin HL, Lasota J. Evaluation of malignancy and prognosis of gastrointestinal stromal tumors: a review. Hum Pathol 2002;33:478–83. Fletcher CD, Berman JJ, Corless C, et al. Diagnosis of gastrointestinal stromal tumors: a consensus approach. Int J Surg Pathol 2002;10:81–9. Emory TS, Sobin LH, Lukes L, Lee DH, O’Leary TJ. Prognosis of gastrointestinal smooth-muscle (stromal) tumors: dependence on anatomic site. Am J Surg Pathol 1999;23:82–7. Goldblum JR, Appelman HD. Stromal tumors of the duodenum. A histologic and immunohistochemical study of 20 cases. Am J Surg Pathol 1995;19:71–80. Amin MB, Ma CK, Linden MD, Kubus JJ, Zarbo RJ. Prognostic value of proliferating cell nuclear antigen index in gastric stromal tumors. Correlation with mitotic count and clinical outcome. Am J Clin Pathol 1993;100:428–32. Panizo-Santos A, Sola I, Vega F, et al. Predicting metastatic risk of gastrointestinal stromal tumors: role of cell proliferation and cell cycle regulatory proteins. Int J Surg Pathol 2000;8:133–44. Wong NA, Young R, Malcomson RD, et al. Prognostic indicators for gastrointestinal stromal tumours: a clinicopathological and immunohistochemical study of 108 resected cases of the stomach. Histopathology 2003;43:118–26. Schneider-Stock R, Boltze C, Lasota J, et al. High prognostic value of p16INK4 alterations in gastrointestinal stromal tumors. J Clin Oncol 2003;21:1688–97. Sabah M, Cummins R, Leader M, Kay E. Loss of heterozygosity of chromosome 9p and loss of p16(INK4A) expres-
M. Sabah et al.
40.
41.
42.
43.
44.
45.
46. 47.
48.
49.
50.
51.
sion are associated with malignant gastrointestinal stromal tumors. Mod Pathol 2004;17:1364–71. Singer S, Rubin BP, Lux ML, et al. Prognostic value of KIT mutation type, mitotic activity, and histologic subtype in gastrointestinal stromal tumors. J Clin Oncol 2002;20: 3898–905. Wardelmann E, Losen I, Hans V, et al. Deletion of Trp-557 and Lys-558 in the juxtamembrane domain of the c-kit protooncogene is associated with metastatic behavior of gastrointestinal stromal tumors. Int J Cancer 2003;106: 887–95. Antonescu CR, Sommer G, Sarran L, et al. Association of KIT exon 9 mutations with nongastric primary site and aggressive behavior: KIT mutation analysis and clinical correlates of 120 gastrointestinal stromal tumors. Clin Cancer Res 2003;9:3329–37. Debiec-Rychter M, Dumez H, Judson I, et al. Use of c-KIT/ PDGFRA mutational analysis to predict the clinical response to imatinib in patients with advanced gastrointestinal stromal tumours entered on phase I and II studies of the EORTC Soft Tissue and Bone Sarcoma Group. Eur J Cancer 2004;40:689–95. Debiec-Rychter M, Lasota J, Sarlomo-Rikala M, Kordek R, Miettinen M. Chromosomal aberrations in malignant gastrointestinal stromal tumors: correlation with c-KIT gene mutation. Cancer Genet Cytogenet 2001;128:24–30. Kim NG, Kim JJ, Ahn JY, et al. Putative chromosomal deletions on 9P, 9Q and 22Q occur preferentially in malignant gastrointestinal stromal tumors. Int J Cancer 2000;85:633–8. Sakurai S, Fukayama M, Kaizaki Y, et al. Telomerase activity in gastrointestinal stromal tumors. Cancer 1998;83:2060–6. Gunther T, Schneider-Stock R, Hackel C, et al. Telomerase activity and expression of hTRT and hTR in gastrointestinal stromal tumors in comparison with extragastrointestinal sarcomas. Clin Cancer Res 2000;6:1811–8. Sabah M, Cummins R, Leader M, Kay E. Expression of human telomerase reverse transcriptase in gastrointestinal stromal tumors occurs preferentially in malignant neoplasms. Hum Pathol 2004;35:1231–5. Dematteo RP, Heinrich MC, El Rifai WM, Demetri G. Clinical management of gastrointestinal stromal tumors: before and after STI-571. Hum Pathol 2002;33:466–77. van Oosterom AT, Judson I, Verweij J, et al. Safety and efficacy of imatinib (STI571) in metastatic gastrointestinal stromal tumours: a phase I study. Lancet 2001;358: 1421–3. Sakamoto KM. Su-11248 Sugen. Curr Opin Investig Drugs 2004;5(12):1329–39.