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Recent advances in the pathology of fibroepithelial tumours of the breast
ARTICLE IN PRESS Current Diagnostic Pathology (2005) 11, 426–434
www.elsevier.com/locate/cdip
REVIEW
Recent advances in the pathology of fibroepithelial tumours of the breast Gary M.K. Tsea,, Puay Hoon Tanb a
Department of Anatomical and Cellular Pathology, Prince of Wales Hospital, Chinese University of Hong Kong, Ngan Shing Street, Shatin, NT, Hong Kong b Department of Pathology, Singapore General Hospital, Outram Road, Singapore 169608, Singapore
KEYWORDS Fibroadenoma; Phyllodes tumour
Summary Fibroepithelial lesions of the breast are biphasic lesions with epithelial and stromal components, as exemplified by fibroadenoma and phyllodes tumour. Fibroadenomas are benign, but a subset of complex fibroadenoma is associated with slightly increased long-term cancer risk. Phyllodes tumour is characterised by a leaflike pattern arising from stromal expansion. It shows a variable degree of malignancy, with a potential for recurrence or metastasis. Conventionally, histological parameters of stromal cellularity, nuclear pleomorphism, overgrowth, mitotic activity and margin configuration are used for grading, but no definitive criteria have been identified to predict the behaviour. Other markers that have been investigated so far include p53, hormonal receptors, proliferation markers, angiogenesis, c-kit (CD117) and CD10 (CALLA), all without clear-cut advantage over histological criteria. There is also emerging histological and molecular evidence that fibroadenoma and phyllodes tumour may be related and epithelial–stromal interaction may play a role in the pathogenesis of these fibroepithelial lesions. & 2005 Elsevier Ltd. All rights reserved.
Introduction Fibroepithelial lesion of the breast is a distinct group of lesions that shows integral epithelial and stromal components. The two major lesions are fibroadenoma (including variants) and phyllodes tumours. The importance of fibroadenomas lies in the fact that they are common. Phyllodes tumours, Corresponding author. Tel.: 852 26322359; fax: 852 26374858.
E-mail address: [email protected] (G.M.K. Tse).
however, have been the subject of many studies, since they show a variable degree of clinical behaviour, ranging from being totally benign to locally recurrent to exhibiting metastatic potential and significant mortality. Histologically, fibroadenomas and phyllodes tumours share the common theme of intimate association of the epithelial and stromal components, with the stromal component being derived exclusively from the interlobular specialised stroma, giving the characteristic myxoid-like appearance.1
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ARTICLE IN PRESS Recent advances in the pathology of fibroepithelial tumours of the breast
Fibroadenoma In fibroadenoma, the typical macroscopic appearance is a sharply circumscribed ovoid mass that is grey white to yellow in colour and the cut surface shows a glistening and lobulated pattern (Fig. 1). The microscopic features are characterised by expansion of the stromal component around epithelial structures (canaliculi). Conventionally, two morphological patterns are recognised. The pericanalicular pattern shows canalicular cuffing by the stroma, whereas the intracanalicular pattern shows projection of stromal nodules into the canaliculi. Both patterns may be present in the same fibroadenoma, or one pattern may predominate, but this distinction has no prognostic significance.2 In addition to this conventional type, some authors 3 also include categories of myxoid fibroadenoma and hamartomatous fibroadenoma. The myxoid fibroadenoma shows large areas of pale hypocellular stroma, which is faint-staining and contains hyaluronic acid. The canaliculi are attenuated and compressed, sometimes devoid of lumen and with a thickened basement membrane,
Figure 1 A typical fibroadenoma, showing an intracanalicular growth pattern with compressed epithelium and a myxoid stroma.
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in contrast to the conventional fibroadenomas. This myxoid variant is thought to be associated with the Carney’s complex. In hamartomatous fibroadenoma, the stroma contains collagen and many fibroblasts, as well as more than usual numbers of lymphocytes and plasma cells. There is a lack of myxoid-staining ground substance in the stroma. The epithelium may show hyperplastic changes. Within a fibroadenoma, many changes may coexist, most of which are of minimal clinical significance. In a large series of 396 fibroadenomas,4 mild to moderate duct hyperplasia, apocrine metaplasia and sclerosing adenosis are observed in about 10–40% of lesions. Other less common changes (5–10%) include florid epithelial hyperplasia and cyst formation. Calcification, pseudoangiomatous stromal changes, papilloma formation and the presence of smooth muscle in the stroma are uncommon (1–5%). The presence of atypical epithelial (ductal or lobular) hyperplasia, ductal and lobular carcinoma in situ or infiltrative carcinoma is distinctly rare, occurring in less than 1% in the same series. A fibroadenoma is termed complex if it possesses any of the following four features: (1) cyst formation greater than 3 mm, (2) sclerosing adenosis, (3) epithelial calcifications and (4) papillary apocrine metaplasia. Complex fibroadenoma (Fig. 2) has a slightly higher relative risk for cancer development, for as long as up to 20 years.5 However, the same group of authors also reported that atypical epithelial hyperplasia within a fibroadenoma does not incur an elevation of long term risk for breast cancer, if the atypical epithelial hyperplasia is localised within the fibroadenoma entirely.6 Other studies have found that age of the patient with fibroadenoma also alters the risk of subsequent cancer development. Women above the age of 40 with fibroadenoma have a higher cancer risk than their younger counterparts.7 The aetiology of fibroadenoma remains elusive, but it can be viewed as a proliferation of the specialised stroma at the terminal ductal lobular units, particularly in a periductal manner.3 The observation of atrophic changes and stromal hyalinisation in post-menopausal women implicates hormonal influences as well. Recently, an increase in fibroadenoma incidence in renal transplant patients under cyclosporine therapy has been reported. The exact underlying mechanism is not fully understood, but it may probably be related to increased transforming growth factor-beta (TGF-ß) synthesis and expression, a mechanism similar to that for the purported aetiology for gingival hypertrophy in these patients.8
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G.M.K. Tse, P. Hoon Tan cellularity is usually high. The behaviour and prognostic implication is similar to conventional fibroadenoma.9
Phyllodes tumour
Figure 2 A complex fibroadenoma, showing cysts and papillary apocrine metaplasia (A), as well as sclerosing adenosis (B), within the lesion.
Juvenile fibroadenoma is a fibroadenoma variant that is endowed with a rapid growth rate and attains a large size. This lesion usually occurs in younger women and the rapid growth may result in distortion of the breast and nipple. Microscopically, it recapitulates the usual fibroadenoma structure with a usually pericanalicular pattern, but there may be florid epithelial hyperplasia and the stromal
Phyllodes tumour is uncommon, occurring much less frequently than fibroadenoma. The real incidence is difficult to estimate, but is probably less than 1% of primary breast tumours.2 There appears to be ethnical differences, with a higher incidence occurring in Asians. In general the patient’s age for phyllodes tumour is about 15–20 years older than that for fibroadenoma. Macroscopically, phyllodes tumour forms a firm lobulated mass with an apparent circumscription. The cut surface is yellowish tan and may occasionally show compressed slit-like spaces with frondlike growth within it. Foci of haemorrhage or necrosis may be seen. Microscopically, phyllodes tumour shares with fibroadenoma the intimate proliferation of the stromal and epithelial components. Compared to fibroadenoma, the degree of stromal proliferation is more prominent, resulting in protrusion of the stroma into the canaliculi, giving a leaf or frond-like appearance, hence the name phyllodes (leaf-like). The microscopic features of phyllodes tumours are very variable and lie in a continuous spectrum, which is labelled as benign at one end and malignant at the other. In general, no single histological criterion can be used in the grading of phyllodes tumours. Instead several histological parameters are assessed, including stromal cellularity, stromal cell atypia, mitotic activity, stromal overgrowth (defined as the absence of epithelial element in the expanded stroma within a low power field), whether the margin is rounded or infiltrative, necrosis and malignant heterologous (osteosarcomatous or chondrosarcomatous) elements.2,10–14 Typically a benign phyllodes tumour (Fig. 3) is diagnosed when there is low stromal cellularity, low mitotic count (less than 3–4 per 10 high power fields), a rounded margin, absence of stromal cell atypia or nuclear pleomorphism, absence of stromal overgrowth and absence of necrosis or malignant heterologous elements. However, a malignant diagnosis is made when there is stromal hypercellularity, significant stromal cell atypia or nuclear pleomorphism, high mitotic count (more than 3–4 per 10 high power fields), stromal overgrowth and infiltrative margin, the presence of necrosis or a malignant heterologous element
ARTICLE IN PRESS Recent advances in the pathology of fibroepithelial tumours of the breast
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Figure 3 A benign phyllodes tumour, with a leaf-like frond lined by epithelium, accompanied by hypercellular stroma.
(Fig. 4). Many phyllodes tumours however do not possess all the features for malignancy and they are labelled as being of borderline malignancy. This division is arbitrary by nature, since using a combination of histological criteria for interpretation is somewhat subjective, as evidenced by the fact that in different large series, the percentage of borderline malignant phyllodes tumours ranges from 12% to up to 26%,2,10–14 thus highlighting the fact that the degree of malignancy in phyllodes tumours is in a continuum. The importance of grading phyllodes tumours into benign and malignant (borderline or frank) lies in the fact that while all grades of phyllodes tumours may recur, the malignant ones may also metastasize. In the literature, the recurrence rate of phyllodes tumours ranges from 10 to 25% for benign phyllodes, up to 32% for phyllodes tumour of borderline malignancy and up to 40% for frankly malignant phyllodes tumours. Distant metastasis has not been reported for benign phyllodes tumour and the incidence is up to 22% in frankly malignant phyllodes tumours.10,12,14–20 Most local recurrence occurs within 2 years of the initial presentation of the tumour and the pathology of the recurrence may by either biphasic (including both epithelial and stromal components), or monophasic, containing only the stromal component.14,20 For distant metastasis, most reported cases occur in systemic organs, with only sporadic reports of a single case of lymph node metastasis in a series of 20 malignant phyllodes tumours with recurrences.16 In addition, distant metastasis may also be preceded by local recurrences.14 In another large series10 of 335 phyllodes tumours with 57 recur-
Figure 4 A malignant phyllodes tumour (A), showing stromal overgrowth (B), which is defined as one low power microscopic field devoid of epithelial elements and (C) stromal cytological atypia with mitoses.
rences (including 43 first, 9 second, 4 third and 1 fourth recurrence), there is no definite relationship between the histological grade of the original and recurrent tumours. Progression from lower grade tumour to higher grade recurrences was noted in 15
ARTICLE IN PRESS 430 tumours (26%), regression from higher grade tumour to lower grade recurrences was noted in six tumours (11%) and the majority (36 recurrent tumours (63%)) were of the same grade as the original tumour. Other features that do not affect the grading may also occur in phyllodes tumours, including epithelial changes, stromal giant cells and pseudoangiomatous stromal changes. Epithelial hyperplasia within phyllodes tumours is very common and in one large series it occurred in 74% of the cases with a mild to moderate degree of epithelial hyperplasia, accounting for the majority of these cases,10 while significant epithelial hyperplasia was noted in 30% in another study.14 Atypical epithelial hyperplasia is less common, ranging from 1.5% to 4% in these series and lobular neoplasia (encompassing atypical lobular hyperplasia and lobular carcinoma in situ) is noted in 0.5–5% in these series. Ductal carcinoma in situ is most uncommon, occurring in less than 1%.10,14 Multinucleated stromal giant cells have also been reported in fibroepithelial lesions of the breast, notably in phyllodes tumours.10,21,22 The reported overall incidence ranged from 9% to 12% and, interestingly, more stromal giant cells are found in phyllodes tumours of higher grade.10,21 These giant cells tend to occur in tight aggregates, usually present in the sub-epithelial regions of high stromal cellularity. They possess five to eight nuclei that are arranged linearly to irregularly. There is no difference in morphology between these giant cells in benign, borderline malignant or frankly malignant phyllodes tumours and their immunohistochemical profile has been shown to be similar to the adjacent stromal cells, implying that the prognosis can be based on the parameters of the stromal cells, irrespective of these multinucleated giant cells.21,22 The presence of pseudoangiomatous stromal hyperplasia (PASH) within the stroma of phyllodes tumours has been described in as many as 70% of phyllodes tumours when one low power field of characteristic slit-like changes in the stroma is used as the cut off. Curiously PASH is shown to be inversely correlated to the tumour grade, thus translating into the finding that PASH in a phyllodes tumour is less likely to be associated with malignancy.10 The major problem in phyllodes tumours is the search for reliable predictors for recurrence or metastases, remembering that most phyllodes tumours are benign and do not adversely affect patients’ outcome. The occasional patients who died of phyllodes tumours are those with malignant disease that recurred relentlessly or metastasized.
G.M.K. Tse, P. Hoon Tan Furthermore, most patients who had recurrences did not develop metastases.12 Hence, in the ideal situation, one would like to identify predictors for metastases of phyllodes tumours. By virtue of the nature of the disease, this study is, by necessity, a difficult one because phyllodes tumour is rare, malignant phyllodes tumours are even rarer and it is very difficult to construct series of substantive sizes suitable for statistical analysis. The results of many large series studying the predictive values of histological parameters are confusing and far from unanimous. In some series, only the histological parameters including the grade, stromal atypia, stromal hypercellularity and margin status,10,16,23 or stromal overgrowth 24 are shown to be correlated to disease recurrence, whereas other authors have also emphasised the importance of complete surgical excision at the initial time of treatment.12 Tumour necrosis and stromal elements other than fibromyxoid stroma were the only two independent prognostic factors identified in another large study25 and tumour size and margin clearance were considered to be the only significant prognostic indicator by other groups.26 Many other authors did not find any role for the histological parameters in tumour recurrences 11,15,18 or any effect on the outcome.13,19,27 In another series,14 stromal overgrowth, high mitotic rate of 415 per 50 high power fields and stromal cytological atypia were identified in malignant phyllodes tumours that metastasized. Given the generally confusing state of affairs in predicting recurrence and metastasis of phyllodes tumours, there have been attempts to look for additional prognostic markers. Some of the current observations are reviewed below. It is prudent to point out that these markers have not been extensively studied and although many show a correlation with the grading of phyllodes tumours, none has the ability to consistently predict the outcome or recurrence. Hence, at this point, their utility would be as a ‘soft sign’ in aiding diagnosis and disease grading.
p53 Mutation of p53 is probably the most extensively studied marker in fibroepithelial breast lesions. p53 is a tumour suppressor gene located on 17p13 and it has been implicated in the regulation of normal cell growth and division, DNA repair and apoptosis. It is found to be extensively altered in breast carcinoma. In phyllodes tumours, the results of p53 protein expression were variable. In general there is
ARTICLE IN PRESS Recent advances in the pathology of fibroepithelial tumours of the breast increased p53 protein expression in higher grade lesions compared to lower grade lesions, irrespective of whether the phyllodes tumours are classified into benign and malignant28 or benign, borderline malignant or frankly malignant.11,29,30 In some studies, fibroadenomas are included and they show either negative or weak staining of p53 in a pattern similar to benign phyllodes tumours.11,28,30 The staining pattern in the malignant phyllodes tumours and, very occasionally, in borderline tumours is characteristic, showing diffuse strong nuclear staining, particularly in the stromal cells that show a higher degree of atypicality and also in the more cellular areas in the sub-epithelial location. The significance of p53 staining in the understanding of the disease aetiology remains elusive. Some authors have demonstrated that p53 expression is associated with tumour grade, prominent stromal overgrowth, stromal nuclear pleomorphism, high stromal mitotic count and an infiltrative margin,29 while others have shown a correlation with mitotic count only, but not with other histological parameters.11 These studies, however, are unable to demonstrate the ability of p53 to predict outcome or recurrences,11,29 or have not addressed the issue.28,30
Hormonal receptors Evaluation of hormonal receptor status is now a standard procedure in the assessment of carcinoma of the breast, as this has a bearing in both the prognosis and the prediction of response to adjuvant endocrine therapy. In phyllodes tumours, oestrogen and progesterone receptors are detected, mainly within the epithelium. Progesterone receptor expression is common, oestrogen receptor expression is less common.31 Oestrogen and progesterone receptor expression has been shown in 43% and 84% of the epithelium and in less than 5% of the stromal cells in a large series of phyllodes tumours.32 For epithelial oestrogen receptor, the expression is high in benign but low in borderline and malignant phyllodes. For epithelial progesterone receptor, the expression is high in both benign and borderline but low in malignant phyllodes. Furthermore, epithelial oestrogen receptor expression shows an inverse correlation with the stromal mitotic count and overlapps with the stromal cell mitotic count in predicting the diagnosis. This observation is particularly interesting as it raises the possibility that the epithelium may play a significant role in triggering the stromal proliferation and this phenomenon may be reflected in the
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subepithelial stromal condensation. How this information furthers our understanding of the aetiology of phyllodes tumour remains uncertain, but it strongly suggests that the epithelial component is an integral part of the phyllodal lesions.
Proliferation markers Ki67 (MIB1) is an immunohistochemical marker for cellular proliferation. It is a non-histone nuclear protein that is present throughout the cell cycle, but it reaches a peak value during the G2 M phase. In a study of MIB1 expression in phyllodes tumours and fibroadenomas,33 it was reported that the MIB1 indices were 2%, 5% and 15%, respectively, for fibroadenoma, benign and malignant phyllodes tumours, with the differences attaining statistical significance. Furthermore, there is good correlation with the conventional grading of phyllodes. Similar findings were echoed in another study involving 46 phyllodes tumours, with malignant phyllodes tumours showing a higher MIB1 expression than borderline than benign phyllodes. Within the benign group, the expression of MIB1 was related to the stromal cellularity, with highly cellular lesions showing higher MIB1 expression.34 The utility of Ki67 in predicting outcome is variable, with studies confirming35,36 and refuting33 its usefulness. Measuring the DNA content and S phase fraction by flow cytometry is another approach taken to assess cellular proliferation. In general, fibroadenomas and benign phyllodes tumours are diploid, with aneuploidy identified in some of the borderline to malignant phyllodes tumours.35,36 The S phase fraction also shows a progressive increase from fibroadenoma to benign, borderline to malignant phyllodes.35 Furthermore, both DNA ploidy36 and S phase fraction35 have been reported as independent prognostic indicators in phyllodes tumours.
Angiogenesis Tumour angiogenesis, as assessed by microvessel density, has been extensively investigated for carcinoma of the breast and has been proposed as a prognostic factor in breast cancer, including in node-negative cancers and in ductal carcinoma in situ. In the domain of fibroepithelial lesions, several studies have been conducted by assessing the microvessel density of the stroma using the ‘hot spot’ method, by counting CD31 positive structures
ARTICLE IN PRESS 432 within a certain number of microscopic fields.37,38 A progressive increase in microvessel density from benign to borderline to malignant phyllodes tumours has been shown37,38 as well as the fact that it is independent of mitotic count, nuclear pleomorphism and stromal overgrowth, suggesting that this may be an important independent predictor for malignancy.37 There appears to be an association between microvessel density in phyllodes tumours and the stromal cellularity, as well as with p53 protein expression of the stromal cells.37 The mechanism for the increased angiogenesis is not fully understood, but preliminary evidence suggests a possible role for vascular endothelial growth factor (VEGF).39
c-kit (CD117) c-kit is a proto-oncogene that encodes a tyrosine kinase receptor and is now considered to be a diagnostic marker for gastrointestinal stromal tumours. It has been shown that there is a progressive increase in c-kit expression from benign to malignant phyllodes, ranging from 5% to 17% in the benign lesions to 46–50% in malignant ones40,41 as demonstrated by immunohistochemistry. The underlying mechanism for c-kit expression remains uncertain, since known activation mutations in gastrointestinal stromal tumours in exons 8–15 and 17 of the c-kit gene have not been demonstrated by direct sequencing in the majority of the c-kit over-expressed phyllodes tumours.40 The potential of tyrosine kinase inhibitor (imatinib mesylate/Gleevec/Glivec) as a treatment modality in malignant phyllodes tumours remains to be explored.
CD10 (CALLA) CD10 (CALLA) has been reported to be useful in the diagnosis of stromal malignancies, particular those of the uterus. In fibroepithelial neoplasms, expression of CD10 has been reported to be significantly increased from a low 3–6% expression in fibroadenoma and benign phyllodes tumours to a high 32–50% in borderline to frank malignant phyllodes tumours.42 This, however, remains a poorly evaluated marker and its role as a diagnostic or prognostic marker requires more extensive evaluation.
Molecular studies in fibroepithelial lesions Not many molecular studies have been performed in phyllodes tumours and in fibroadenomas and
G.M.K. Tse, P. Hoon Tan many in the literature are case reports. Most of the molecular studies attempt to answer either of the following two questions: (1) are there any cytogenetic abnormalities present in these lesions and (2) what is the clonality of the epithelial and the stromal components in these lesions and can a relationship or progression be demonstrated between fibroadenoma and phyllodes tumour? Comparative genomic hybridisation (CGH) has been used to delineate the cytogenetic abnormalities of phyllodes tumour and it has been reported that 1q gain, 3p loss, 7q gain, 6q loss and 3q loss are the most common changes detected and there is also evidence that 1q gain may be associated with recurrent disease in phyllodes tumours.43,44 3p loss has been described in benign, atypical and malignant breast lesions and one of the most commonly deleted regions has been mapped to the FHIT gene in the 3p12-14 region. Regarding the clonality of fibroepithelial lesions, fibroadenomas are polyclonal in both the epithelial and stromal components, whereas in phyllodes tumours, the epithelial component is polyclonal but the stromal component is monoclonal,45,46 indicating that phyllodes tumour is a neoplastic stromal lesion, but not fibroadenoma. Recently there is new evidence that shows distinct clonality in the epithelial and stromal components of phyllodes tumour, implying that the epithelial component may also be neoplastic.44 To date, clonality studies have also provided evidence of a possible link between fibroadenoma and phyllodes tumours. In a very interesting clonality study of 45 fibroadenomas, it was found that while most of the fibroadenomas were polyclonal, two possessed monoclonal stromal component, while the histological correlate of one case showed distinct phyllodes tumour-like features in part of the lesion and the other case showed complex fibroadenoma morphology.47 In addition, there is strong evidence that fibroadenomas that are monoclonal may recur as phyllodes tumour, which demonstrates the same pattern of allelic inactivation,48,indicating that some ‘fibroadenomas’ are neoplastic at the outset and may behave more like a phyllodes tumour, resulting in recurrence with the same allelic inactivation pattern. Evidence of stromal progression has also been obtained in a PCR-based study,46 which showed that while the stroma of fibroadenoma and phyllodes tumours were polyclonal and monoclonal, respectively, foci of phyllodes-like stromal expansion within the fibroadenomas were monoclonal. These data are early evidence to suggest that an ‘intermediate lesion’ exists between fibroadenoma
ARTICLE IN PRESS Recent advances in the pathology of fibroepithelial tumours of the breast and phyllodes tumour, occurring as foci of phyllodal stromal pattern within an otherwise unremarkable fibroadenoma. Clonality studies are supportive of this postulation. Lastly, a discussion of fibroepithelial lesions would be incomplete without mentioning the concept of epithelial–stromal interaction. In a pioneer study, it has been shown that in fibroepithelial lesions, mitoses of the stromal cell tend to occur close to the epithelial element, suggesting that stromal growth is dependent on the epithelium.49 The finding of distinct molecular alterations in the epithelial and stromal components in phyllodes tumour,44 as well as the demonstration of a correlation between epithelial hormonal receptor status and the grade of the stromal component,32 have also lent weight to the epithelial contribution in the pathogenesis of phyllodes tumour. Recently an association between stromal beta-catenin with epithelial Wnt5a expression has been reported 50 and it is believed that in phyllodes tumour, the progression to malignancy results from stromal independence from the epithelium. This concept may represent a major step in our understanding of this group of biphasic lesions and warrants further detailed studies.
Practice points
Complex fibroadenomas show at least one of the following histological features: sclerosing adenosis, papillary apocrine metaplasia, cysts and epithelial calcifications. They have a slightly higher relative risk for cancer development compared with conventional fibroadenomas Phyllodes tumours are distinguished from fibroadenomas by their characteristic leaflike pattern accompanied by stromal hypercellularity Phyllodes tumours are graded into benign, borderline and malignant categories based on a constellation of histological changes that include stromal cellularity, mitotic count, stromal cytological atypia, stromal overgrowth and the nature of the margins (pushing versus permeative) All phyllodes tumours may recur and those of borderline or frank malignancy have a potential for metastases, with the latter having a higher metastastic potential Prediction of recurrence or metastasis based on histological parameters is still controversial and some authors have concluded that complete surgical excision is of
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key importance in the management of phyllodes tumours Biological markers do not, as yet, play an established role in determining the behaviour of phyllodes tumours; although studies on p53, proliferation markers, angiogenesis and CD117 in these tumours have been and are being carried out Future research in these biphasic tumours includes focusing on interactions between the epithelium and stroma, interrogating their molecular relationship and providing further insight into the pathogenesis of these lesions
References 1. Lerwill MF. Biphasic lesions of the breast. Sem Diagn Pathol 2004;21:48–56. 2. Elston CW, Ellis IO. The breast. In: Systemic pathology, vol. 13, 3rd ed. Edinburgh: Churchill Livingstone; 2000. p. 147–86. 3. Koerner FC, O’Connell JX. Fibroadenoma: morphological observations and a theory of pathogenesis. Pathol Annu 1994;29:1–19. 4. Kuijper A, Mommers E, van der Wall E, van Diest PJ. Histopathology of fibroadenoma of the breast. Am J Clin Pathol 2001;115:736–42. 5. Dupont WD, Page DL, Parl FF, et al. Long-term risk of breast cancer in women with fibroadenoma. N Engl J Med 1994; 331:10–5. 6. Carter BA, Page DL, Schuyler P, et al. No elevation in long term breast carcinoma risk for women with fibroadenomas that contain atypical hyperplasia. Cancer 2001;92:30–6. 7. Shabtai M, Saavedra-Malinger P, Shabtai EL, et al. Fibroadenoma of the breast: analysis of associated pathological entities—a different risk marker in different age groups for concurrent breast cancer. Isr Med Assoc J 2001;3:813–7. 8. Sangthawan P, Fox J, Atkins RC, Kerr PG. Increased incidence of benign breast disease in female renal transplant patients receiving cyclosporin. ANZ J Surg 2002;72:222–5. 9. Pike AM, Oberman HA. Juvenile (cellular) adenofibromas. A clinicopathologic study. Am J Surg Pathol 1985;9:2891–905. 10. Tan PH, Jayabaskar T, Chuah KL, et al. Phyllodes tumours of the breast. The role of pathologic parameters. Am J Clin Pathol 2005;123:529–40. 11. Tse GM, Putti TC, Kung FY, et al. Increased p53 protein expression in malignant mammary phyllodes tumours. Mod Pathol 2002;15:734–40. 12. Moffat CJ, Pinders SE, Dixon AR, Elston CW, Blamey RW, Ellis IO. Phyllodes tumours of the breast: a clinicopathological review of thirty-two cases. Histopathology 1995;27:205–18. 13. Parkers SJ, Harries SA. Phyllodes tumours. Postgrad Med J 2001;77:428–35. 14. Grimes MM. Cystosarcoma phyllodes of the breast: histological features, flow cytometric analysis, and clinical correlation. Mod Pathol 1992;5:232–9. 15. Mokbel K, Price RK, Mostafa A, Wells CA, Carpenter R. Phyllodes tumour of the breast: a retrospective analysis of 30 cases. Breast 1999;8:278–81.
ARTICLE IN PRESS 434 16. Reinfuss M, Mitus J, Smolak K, Stelmach A. Malignant phyllodes tumours of the breast. A clinical and pathological analysis of 55 cases. Eur J Cancer 1993;29A:1252–6. 17. Staren ED, Lynch G, Boyle C, Witt TR, Bines SD. Malignant cystosarcoma phyllodes. Am Surg 1994;60:583–5. 18. Ciatto S, Bonardi R, Cataliotti L, Cardona G. Phyllodes tumour of the breast: a multicenter series of 59 cases. Coordinating Center and Writing Committee of FONCAM (National Task Force for Breast Cancer), Italy. Eur J Surg Oncol 1992;18:545–9. 19. Geisler DP, Boyle MJ, Malnar KF, et al. Phyllodes tumours of the breast: a review of 32 cases. Am Surg 2000;66:360–6. 20. Bennett IC, Khan A, De Freitas R, Chaudary MA, Millis RR. Phyllodes tumours: a clinicopathological review of 30 cases. Aust NZ J Surg 1992;62:628–33. 21. Tse GM, Law BK, Chan KF, Ma TK. Multinucleated stromal giant cells in mammary phyllodes tumours. Pathology 2001; 33:153–6. 22. Powell CM, Cranor ML, Rosen PP. Multinucleated stromal giant cells in mammary fibroepithelial neoplasms. A study of 11 patients. Arch Pathol Lab Med 1994;118:912–6. 23. Reinfuss M, Mitus J, Duda K, Stelmach A, Rys J, Smolak K. The treatment and prognosis of patients with phyllodes tumour of the breast: an analysis of 170 cases. Cancer 1996;77:910–6. 24. Hawkins RE, Schofield JB, Fisher C, Wiltshaw E, McKinna JA. The clinical and histological criteria that predict metastases from cystosarcoma phyllodes. Cancer 1992;69:141–7. 25. Cohn-Cedermark G, Rutqvist LE, Rosendahl I, Silfversward C. Prognostic factors in cystosarcoma phyllodes. A clinicopathologic study of 77 patients. Cancer 1991;68:2017–22. 26. Kapiris I, Nasiri N, A’Hern R, Healy V, Gui GP. Outcome and predictive factors of local recurrence and distant metastases following primary surgical treatment of high-grade malignant phyllodes tumours of the breast. Eur J Surg Oncol 2001;27:723–30. 27. Keelan PA, Myers JL, Wold LE, Katzmann JA, Gibney DJ. Phyllodes tumour: clinicopathologic review of 60 patients and flow cytometric analysis in 30 patients. Hum Pathol 1992;23:1048–54. 28. Millar EK, Beretov J, Marr P, et al. Malignant phyllodes tumours of the breast display increased stromal p53 protein expression. Histopathology 1999;34:491–6. 29. Feakins RM, Mulcahy HE, Nickols CD, Wells CA. p53 expression in phyllodes tumours is associated with histological features of malignancy but does not predict outcome. Histopathology 1999;35:162–9. 30. Kuenen-Boumeester V, Henzen-Logmans SC, Timmermans MM, et al. Altered expression of p53 and its regulated proteins in phyllodes tumours of the breast. J Pathol 1999;189:169–75. 31. Umekita Y, Yoshida H. Immunohistochemical study of hormone receptor and hormone-regulated protein expression in phyllodes tumour: comparison with fibroadenoma. Virchows Arch 1998;433:311–4. 32. Tse GM, Lee CS, Kung FY, et al. Hormonal receptors expression in epithelial cells of mammary phyllodes tumours correlates with pathologic grade of the tumour: a multicenter study of 143 cases. Am J Clin Pathol 2002;118:522–6. 33. Kocova L, Skalova A, Fakan F, Rousarova M. Phyllodes tumour of the breast: immunohistochemical study of 37 tumours using MIB1 antibody. Pathol Res Pract 1998;194:97–104.
G.M.K. Tse, P. Hoon Tan 34. Umekita Y, Yoshida H. Immunohistochemical study of MIB1 expression in phyllodes tumour and fibroadenoma. Pathol Int 1999;49:807–10. 35. Niezabitowski A, Lackowska B, Rys J, et al. Prognostic evaluation of proliferative activity and DNA content in the phyllodes tumour of the breast: immunohistochemical and flow cytometric study of 118 cases. Breast Cancer Res Treat 2001;65:77–85. 36. el-Naggar AK, Ro JY, McLemore D, Garnsy L. DNA content and proliferative activity of cystosarcoma phyllodes of the breast. Potential prognostic significance. Am J Clin Pathol 1990;93:480–5. 37. Tse GM, Lui PC, Scolyer RA, et al. Tumour angiogenesis and p53 protein expression in mammary phyllodes tumours. Mod Pathol 2003;16:1007–13. 38. Tse GM, Ma TK, Chan KF, et al. Increased microvessel density in malignant and borderline mammary phyllodes tumours. Histopathology 2001;38:567–70. 39. Tse GM, Lui PC, Lee CS, et al. Stromal expression of vascular endothelial growth factor correlates with tumour grade and microvessel density in mammary phyllodes tumours: a multicenter study of 185 cases. Hum Pathol 2004;35: 1053–7. 40. Sawyer EJ, Poulsom R, Hunt FT, et al. Malignant phyllodes tumours show stromal overexpression of c-myc and c-kit. J Pathol 2003;200:59–64. 41. Tse GM, Putti TC, Lui PC, et al. Increased c-kit (CD117) expression in malignant mammary phyllodes tumours. Mod Pathol 2004;17:827–31. 42. Tse GM, Tsang AK, Putti TC, et al. Stromal CD10 expression in mammary fibroadenomas and phyllodes tumours. J Clin Pathol 2005;58:185–9. 43. Lu YJ, Birdsall S, Osin P, Gusterson B, Shipley J. Phyllodes tumours of the breast analyzed by comparative genomic hybridization and association of increased 1q copy number with stromal overgrowth and recurrence. Genes Chromosomes Cancer 1997;20:275–81. 44. Sawyer EJ, Hanby AM, Ellis P, et al. Molecular analysis of phyllodes tumours reveals distinct changes in the epithelial and stromal components. Am J Pathol 2000;156: 1093–8. 45. Noguchi S, Motomura K, Inaji H, Imaoka S, Koyama H. Clonal analysis of fibroadenoma and phyllodes tumour of the breast. Cancer Res 1993;53:4071–4. 46. Kuijper A, Buerger H, Simon R, et al. Analysis of the progression of fibroepithelial tumours of the breast by PCRbased clonality assay. J Pathol 2002;197:575–81. 47. Kasami M, Vnencak-Jones CL, Manning S, Dupont WD, Jensen RA, Page DL. Monoclonality in fibroadenomas with complex histology and phyllodal features. Breast Cancer Res Treat 1998;50:185–91. 48. Noguchi S, Yokouchi H, Aihara T, et al. Progression of fibroadenoma to phyllodes tumour demonstrated by clonal analysis. Cancer 1995;76:1779–85. 49. Sawhney N, Garrahan N, Douglas-Jones AG, Williams ED. Epithelial–stromal interactions in tumours. A morphologic study of fibroepithelial tumours of the breast. Cancer 1992;70:2115–20. 50. Sawyer EJ, Hanby AM, Rowan AJ, et al. The Wnt pathway, epithelial–stromal interactions, and malignant progression in phyllodes tumours. J Pathol 2002;196:437–44.
www.elsevier.com/locate/cdip
REVIEW
Recent advances in the pathology of fibroepithelial tumours of the breast Gary M.K. Tsea,, Puay Hoon Tanb a
Department of Anatomical and Cellular Pathology, Prince of Wales Hospital, Chinese University of Hong Kong, Ngan Shing Street, Shatin, NT, Hong Kong b Department of Pathology, Singapore General Hospital, Outram Road, Singapore 169608, Singapore
KEYWORDS Fibroadenoma; Phyllodes tumour
Summary Fibroepithelial lesions of the breast are biphasic lesions with epithelial and stromal components, as exemplified by fibroadenoma and phyllodes tumour. Fibroadenomas are benign, but a subset of complex fibroadenoma is associated with slightly increased long-term cancer risk. Phyllodes tumour is characterised by a leaflike pattern arising from stromal expansion. It shows a variable degree of malignancy, with a potential for recurrence or metastasis. Conventionally, histological parameters of stromal cellularity, nuclear pleomorphism, overgrowth, mitotic activity and margin configuration are used for grading, but no definitive criteria have been identified to predict the behaviour. Other markers that have been investigated so far include p53, hormonal receptors, proliferation markers, angiogenesis, c-kit (CD117) and CD10 (CALLA), all without clear-cut advantage over histological criteria. There is also emerging histological and molecular evidence that fibroadenoma and phyllodes tumour may be related and epithelial–stromal interaction may play a role in the pathogenesis of these fibroepithelial lesions. & 2005 Elsevier Ltd. All rights reserved.
Introduction Fibroepithelial lesion of the breast is a distinct group of lesions that shows integral epithelial and stromal components. The two major lesions are fibroadenoma (including variants) and phyllodes tumours. The importance of fibroadenomas lies in the fact that they are common. Phyllodes tumours, Corresponding author. Tel.: 852 26322359; fax: 852 26374858.
E-mail address: [email protected] (G.M.K. Tse).
however, have been the subject of many studies, since they show a variable degree of clinical behaviour, ranging from being totally benign to locally recurrent to exhibiting metastatic potential and significant mortality. Histologically, fibroadenomas and phyllodes tumours share the common theme of intimate association of the epithelial and stromal components, with the stromal component being derived exclusively from the interlobular specialised stroma, giving the characteristic myxoid-like appearance.1
0968-6053/$ - see front matter & 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.cdip.2005.08.007
ARTICLE IN PRESS Recent advances in the pathology of fibroepithelial tumours of the breast
Fibroadenoma In fibroadenoma, the typical macroscopic appearance is a sharply circumscribed ovoid mass that is grey white to yellow in colour and the cut surface shows a glistening and lobulated pattern (Fig. 1). The microscopic features are characterised by expansion of the stromal component around epithelial structures (canaliculi). Conventionally, two morphological patterns are recognised. The pericanalicular pattern shows canalicular cuffing by the stroma, whereas the intracanalicular pattern shows projection of stromal nodules into the canaliculi. Both patterns may be present in the same fibroadenoma, or one pattern may predominate, but this distinction has no prognostic significance.2 In addition to this conventional type, some authors 3 also include categories of myxoid fibroadenoma and hamartomatous fibroadenoma. The myxoid fibroadenoma shows large areas of pale hypocellular stroma, which is faint-staining and contains hyaluronic acid. The canaliculi are attenuated and compressed, sometimes devoid of lumen and with a thickened basement membrane,
Figure 1 A typical fibroadenoma, showing an intracanalicular growth pattern with compressed epithelium and a myxoid stroma.
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in contrast to the conventional fibroadenomas. This myxoid variant is thought to be associated with the Carney’s complex. In hamartomatous fibroadenoma, the stroma contains collagen and many fibroblasts, as well as more than usual numbers of lymphocytes and plasma cells. There is a lack of myxoid-staining ground substance in the stroma. The epithelium may show hyperplastic changes. Within a fibroadenoma, many changes may coexist, most of which are of minimal clinical significance. In a large series of 396 fibroadenomas,4 mild to moderate duct hyperplasia, apocrine metaplasia and sclerosing adenosis are observed in about 10–40% of lesions. Other less common changes (5–10%) include florid epithelial hyperplasia and cyst formation. Calcification, pseudoangiomatous stromal changes, papilloma formation and the presence of smooth muscle in the stroma are uncommon (1–5%). The presence of atypical epithelial (ductal or lobular) hyperplasia, ductal and lobular carcinoma in situ or infiltrative carcinoma is distinctly rare, occurring in less than 1% in the same series. A fibroadenoma is termed complex if it possesses any of the following four features: (1) cyst formation greater than 3 mm, (2) sclerosing adenosis, (3) epithelial calcifications and (4) papillary apocrine metaplasia. Complex fibroadenoma (Fig. 2) has a slightly higher relative risk for cancer development, for as long as up to 20 years.5 However, the same group of authors also reported that atypical epithelial hyperplasia within a fibroadenoma does not incur an elevation of long term risk for breast cancer, if the atypical epithelial hyperplasia is localised within the fibroadenoma entirely.6 Other studies have found that age of the patient with fibroadenoma also alters the risk of subsequent cancer development. Women above the age of 40 with fibroadenoma have a higher cancer risk than their younger counterparts.7 The aetiology of fibroadenoma remains elusive, but it can be viewed as a proliferation of the specialised stroma at the terminal ductal lobular units, particularly in a periductal manner.3 The observation of atrophic changes and stromal hyalinisation in post-menopausal women implicates hormonal influences as well. Recently, an increase in fibroadenoma incidence in renal transplant patients under cyclosporine therapy has been reported. The exact underlying mechanism is not fully understood, but it may probably be related to increased transforming growth factor-beta (TGF-ß) synthesis and expression, a mechanism similar to that for the purported aetiology for gingival hypertrophy in these patients.8
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G.M.K. Tse, P. Hoon Tan cellularity is usually high. The behaviour and prognostic implication is similar to conventional fibroadenoma.9
Phyllodes tumour
Figure 2 A complex fibroadenoma, showing cysts and papillary apocrine metaplasia (A), as well as sclerosing adenosis (B), within the lesion.
Juvenile fibroadenoma is a fibroadenoma variant that is endowed with a rapid growth rate and attains a large size. This lesion usually occurs in younger women and the rapid growth may result in distortion of the breast and nipple. Microscopically, it recapitulates the usual fibroadenoma structure with a usually pericanalicular pattern, but there may be florid epithelial hyperplasia and the stromal
Phyllodes tumour is uncommon, occurring much less frequently than fibroadenoma. The real incidence is difficult to estimate, but is probably less than 1% of primary breast tumours.2 There appears to be ethnical differences, with a higher incidence occurring in Asians. In general the patient’s age for phyllodes tumour is about 15–20 years older than that for fibroadenoma. Macroscopically, phyllodes tumour forms a firm lobulated mass with an apparent circumscription. The cut surface is yellowish tan and may occasionally show compressed slit-like spaces with frondlike growth within it. Foci of haemorrhage or necrosis may be seen. Microscopically, phyllodes tumour shares with fibroadenoma the intimate proliferation of the stromal and epithelial components. Compared to fibroadenoma, the degree of stromal proliferation is more prominent, resulting in protrusion of the stroma into the canaliculi, giving a leaf or frond-like appearance, hence the name phyllodes (leaf-like). The microscopic features of phyllodes tumours are very variable and lie in a continuous spectrum, which is labelled as benign at one end and malignant at the other. In general, no single histological criterion can be used in the grading of phyllodes tumours. Instead several histological parameters are assessed, including stromal cellularity, stromal cell atypia, mitotic activity, stromal overgrowth (defined as the absence of epithelial element in the expanded stroma within a low power field), whether the margin is rounded or infiltrative, necrosis and malignant heterologous (osteosarcomatous or chondrosarcomatous) elements.2,10–14 Typically a benign phyllodes tumour (Fig. 3) is diagnosed when there is low stromal cellularity, low mitotic count (less than 3–4 per 10 high power fields), a rounded margin, absence of stromal cell atypia or nuclear pleomorphism, absence of stromal overgrowth and absence of necrosis or malignant heterologous elements. However, a malignant diagnosis is made when there is stromal hypercellularity, significant stromal cell atypia or nuclear pleomorphism, high mitotic count (more than 3–4 per 10 high power fields), stromal overgrowth and infiltrative margin, the presence of necrosis or a malignant heterologous element
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Figure 3 A benign phyllodes tumour, with a leaf-like frond lined by epithelium, accompanied by hypercellular stroma.
(Fig. 4). Many phyllodes tumours however do not possess all the features for malignancy and they are labelled as being of borderline malignancy. This division is arbitrary by nature, since using a combination of histological criteria for interpretation is somewhat subjective, as evidenced by the fact that in different large series, the percentage of borderline malignant phyllodes tumours ranges from 12% to up to 26%,2,10–14 thus highlighting the fact that the degree of malignancy in phyllodes tumours is in a continuum. The importance of grading phyllodes tumours into benign and malignant (borderline or frank) lies in the fact that while all grades of phyllodes tumours may recur, the malignant ones may also metastasize. In the literature, the recurrence rate of phyllodes tumours ranges from 10 to 25% for benign phyllodes, up to 32% for phyllodes tumour of borderline malignancy and up to 40% for frankly malignant phyllodes tumours. Distant metastasis has not been reported for benign phyllodes tumour and the incidence is up to 22% in frankly malignant phyllodes tumours.10,12,14–20 Most local recurrence occurs within 2 years of the initial presentation of the tumour and the pathology of the recurrence may by either biphasic (including both epithelial and stromal components), or monophasic, containing only the stromal component.14,20 For distant metastasis, most reported cases occur in systemic organs, with only sporadic reports of a single case of lymph node metastasis in a series of 20 malignant phyllodes tumours with recurrences.16 In addition, distant metastasis may also be preceded by local recurrences.14 In another large series10 of 335 phyllodes tumours with 57 recur-
Figure 4 A malignant phyllodes tumour (A), showing stromal overgrowth (B), which is defined as one low power microscopic field devoid of epithelial elements and (C) stromal cytological atypia with mitoses.
rences (including 43 first, 9 second, 4 third and 1 fourth recurrence), there is no definite relationship between the histological grade of the original and recurrent tumours. Progression from lower grade tumour to higher grade recurrences was noted in 15
ARTICLE IN PRESS 430 tumours (26%), regression from higher grade tumour to lower grade recurrences was noted in six tumours (11%) and the majority (36 recurrent tumours (63%)) were of the same grade as the original tumour. Other features that do not affect the grading may also occur in phyllodes tumours, including epithelial changes, stromal giant cells and pseudoangiomatous stromal changes. Epithelial hyperplasia within phyllodes tumours is very common and in one large series it occurred in 74% of the cases with a mild to moderate degree of epithelial hyperplasia, accounting for the majority of these cases,10 while significant epithelial hyperplasia was noted in 30% in another study.14 Atypical epithelial hyperplasia is less common, ranging from 1.5% to 4% in these series and lobular neoplasia (encompassing atypical lobular hyperplasia and lobular carcinoma in situ) is noted in 0.5–5% in these series. Ductal carcinoma in situ is most uncommon, occurring in less than 1%.10,14 Multinucleated stromal giant cells have also been reported in fibroepithelial lesions of the breast, notably in phyllodes tumours.10,21,22 The reported overall incidence ranged from 9% to 12% and, interestingly, more stromal giant cells are found in phyllodes tumours of higher grade.10,21 These giant cells tend to occur in tight aggregates, usually present in the sub-epithelial regions of high stromal cellularity. They possess five to eight nuclei that are arranged linearly to irregularly. There is no difference in morphology between these giant cells in benign, borderline malignant or frankly malignant phyllodes tumours and their immunohistochemical profile has been shown to be similar to the adjacent stromal cells, implying that the prognosis can be based on the parameters of the stromal cells, irrespective of these multinucleated giant cells.21,22 The presence of pseudoangiomatous stromal hyperplasia (PASH) within the stroma of phyllodes tumours has been described in as many as 70% of phyllodes tumours when one low power field of characteristic slit-like changes in the stroma is used as the cut off. Curiously PASH is shown to be inversely correlated to the tumour grade, thus translating into the finding that PASH in a phyllodes tumour is less likely to be associated with malignancy.10 The major problem in phyllodes tumours is the search for reliable predictors for recurrence or metastases, remembering that most phyllodes tumours are benign and do not adversely affect patients’ outcome. The occasional patients who died of phyllodes tumours are those with malignant disease that recurred relentlessly or metastasized.
G.M.K. Tse, P. Hoon Tan Furthermore, most patients who had recurrences did not develop metastases.12 Hence, in the ideal situation, one would like to identify predictors for metastases of phyllodes tumours. By virtue of the nature of the disease, this study is, by necessity, a difficult one because phyllodes tumour is rare, malignant phyllodes tumours are even rarer and it is very difficult to construct series of substantive sizes suitable for statistical analysis. The results of many large series studying the predictive values of histological parameters are confusing and far from unanimous. In some series, only the histological parameters including the grade, stromal atypia, stromal hypercellularity and margin status,10,16,23 or stromal overgrowth 24 are shown to be correlated to disease recurrence, whereas other authors have also emphasised the importance of complete surgical excision at the initial time of treatment.12 Tumour necrosis and stromal elements other than fibromyxoid stroma were the only two independent prognostic factors identified in another large study25 and tumour size and margin clearance were considered to be the only significant prognostic indicator by other groups.26 Many other authors did not find any role for the histological parameters in tumour recurrences 11,15,18 or any effect on the outcome.13,19,27 In another series,14 stromal overgrowth, high mitotic rate of 415 per 50 high power fields and stromal cytological atypia were identified in malignant phyllodes tumours that metastasized. Given the generally confusing state of affairs in predicting recurrence and metastasis of phyllodes tumours, there have been attempts to look for additional prognostic markers. Some of the current observations are reviewed below. It is prudent to point out that these markers have not been extensively studied and although many show a correlation with the grading of phyllodes tumours, none has the ability to consistently predict the outcome or recurrence. Hence, at this point, their utility would be as a ‘soft sign’ in aiding diagnosis and disease grading.
p53 Mutation of p53 is probably the most extensively studied marker in fibroepithelial breast lesions. p53 is a tumour suppressor gene located on 17p13 and it has been implicated in the regulation of normal cell growth and division, DNA repair and apoptosis. It is found to be extensively altered in breast carcinoma. In phyllodes tumours, the results of p53 protein expression were variable. In general there is
ARTICLE IN PRESS Recent advances in the pathology of fibroepithelial tumours of the breast increased p53 protein expression in higher grade lesions compared to lower grade lesions, irrespective of whether the phyllodes tumours are classified into benign and malignant28 or benign, borderline malignant or frankly malignant.11,29,30 In some studies, fibroadenomas are included and they show either negative or weak staining of p53 in a pattern similar to benign phyllodes tumours.11,28,30 The staining pattern in the malignant phyllodes tumours and, very occasionally, in borderline tumours is characteristic, showing diffuse strong nuclear staining, particularly in the stromal cells that show a higher degree of atypicality and also in the more cellular areas in the sub-epithelial location. The significance of p53 staining in the understanding of the disease aetiology remains elusive. Some authors have demonstrated that p53 expression is associated with tumour grade, prominent stromal overgrowth, stromal nuclear pleomorphism, high stromal mitotic count and an infiltrative margin,29 while others have shown a correlation with mitotic count only, but not with other histological parameters.11 These studies, however, are unable to demonstrate the ability of p53 to predict outcome or recurrences,11,29 or have not addressed the issue.28,30
Hormonal receptors Evaluation of hormonal receptor status is now a standard procedure in the assessment of carcinoma of the breast, as this has a bearing in both the prognosis and the prediction of response to adjuvant endocrine therapy. In phyllodes tumours, oestrogen and progesterone receptors are detected, mainly within the epithelium. Progesterone receptor expression is common, oestrogen receptor expression is less common.31 Oestrogen and progesterone receptor expression has been shown in 43% and 84% of the epithelium and in less than 5% of the stromal cells in a large series of phyllodes tumours.32 For epithelial oestrogen receptor, the expression is high in benign but low in borderline and malignant phyllodes. For epithelial progesterone receptor, the expression is high in both benign and borderline but low in malignant phyllodes. Furthermore, epithelial oestrogen receptor expression shows an inverse correlation with the stromal mitotic count and overlapps with the stromal cell mitotic count in predicting the diagnosis. This observation is particularly interesting as it raises the possibility that the epithelium may play a significant role in triggering the stromal proliferation and this phenomenon may be reflected in the
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subepithelial stromal condensation. How this information furthers our understanding of the aetiology of phyllodes tumour remains uncertain, but it strongly suggests that the epithelial component is an integral part of the phyllodal lesions.
Proliferation markers Ki67 (MIB1) is an immunohistochemical marker for cellular proliferation. It is a non-histone nuclear protein that is present throughout the cell cycle, but it reaches a peak value during the G2 M phase. In a study of MIB1 expression in phyllodes tumours and fibroadenomas,33 it was reported that the MIB1 indices were 2%, 5% and 15%, respectively, for fibroadenoma, benign and malignant phyllodes tumours, with the differences attaining statistical significance. Furthermore, there is good correlation with the conventional grading of phyllodes. Similar findings were echoed in another study involving 46 phyllodes tumours, with malignant phyllodes tumours showing a higher MIB1 expression than borderline than benign phyllodes. Within the benign group, the expression of MIB1 was related to the stromal cellularity, with highly cellular lesions showing higher MIB1 expression.34 The utility of Ki67 in predicting outcome is variable, with studies confirming35,36 and refuting33 its usefulness. Measuring the DNA content and S phase fraction by flow cytometry is another approach taken to assess cellular proliferation. In general, fibroadenomas and benign phyllodes tumours are diploid, with aneuploidy identified in some of the borderline to malignant phyllodes tumours.35,36 The S phase fraction also shows a progressive increase from fibroadenoma to benign, borderline to malignant phyllodes.35 Furthermore, both DNA ploidy36 and S phase fraction35 have been reported as independent prognostic indicators in phyllodes tumours.
Angiogenesis Tumour angiogenesis, as assessed by microvessel density, has been extensively investigated for carcinoma of the breast and has been proposed as a prognostic factor in breast cancer, including in node-negative cancers and in ductal carcinoma in situ. In the domain of fibroepithelial lesions, several studies have been conducted by assessing the microvessel density of the stroma using the ‘hot spot’ method, by counting CD31 positive structures
ARTICLE IN PRESS 432 within a certain number of microscopic fields.37,38 A progressive increase in microvessel density from benign to borderline to malignant phyllodes tumours has been shown37,38 as well as the fact that it is independent of mitotic count, nuclear pleomorphism and stromal overgrowth, suggesting that this may be an important independent predictor for malignancy.37 There appears to be an association between microvessel density in phyllodes tumours and the stromal cellularity, as well as with p53 protein expression of the stromal cells.37 The mechanism for the increased angiogenesis is not fully understood, but preliminary evidence suggests a possible role for vascular endothelial growth factor (VEGF).39
c-kit (CD117) c-kit is a proto-oncogene that encodes a tyrosine kinase receptor and is now considered to be a diagnostic marker for gastrointestinal stromal tumours. It has been shown that there is a progressive increase in c-kit expression from benign to malignant phyllodes, ranging from 5% to 17% in the benign lesions to 46–50% in malignant ones40,41 as demonstrated by immunohistochemistry. The underlying mechanism for c-kit expression remains uncertain, since known activation mutations in gastrointestinal stromal tumours in exons 8–15 and 17 of the c-kit gene have not been demonstrated by direct sequencing in the majority of the c-kit over-expressed phyllodes tumours.40 The potential of tyrosine kinase inhibitor (imatinib mesylate/Gleevec/Glivec) as a treatment modality in malignant phyllodes tumours remains to be explored.
CD10 (CALLA) CD10 (CALLA) has been reported to be useful in the diagnosis of stromal malignancies, particular those of the uterus. In fibroepithelial neoplasms, expression of CD10 has been reported to be significantly increased from a low 3–6% expression in fibroadenoma and benign phyllodes tumours to a high 32–50% in borderline to frank malignant phyllodes tumours.42 This, however, remains a poorly evaluated marker and its role as a diagnostic or prognostic marker requires more extensive evaluation.
Molecular studies in fibroepithelial lesions Not many molecular studies have been performed in phyllodes tumours and in fibroadenomas and
G.M.K. Tse, P. Hoon Tan many in the literature are case reports. Most of the molecular studies attempt to answer either of the following two questions: (1) are there any cytogenetic abnormalities present in these lesions and (2) what is the clonality of the epithelial and the stromal components in these lesions and can a relationship or progression be demonstrated between fibroadenoma and phyllodes tumour? Comparative genomic hybridisation (CGH) has been used to delineate the cytogenetic abnormalities of phyllodes tumour and it has been reported that 1q gain, 3p loss, 7q gain, 6q loss and 3q loss are the most common changes detected and there is also evidence that 1q gain may be associated with recurrent disease in phyllodes tumours.43,44 3p loss has been described in benign, atypical and malignant breast lesions and one of the most commonly deleted regions has been mapped to the FHIT gene in the 3p12-14 region. Regarding the clonality of fibroepithelial lesions, fibroadenomas are polyclonal in both the epithelial and stromal components, whereas in phyllodes tumours, the epithelial component is polyclonal but the stromal component is monoclonal,45,46 indicating that phyllodes tumour is a neoplastic stromal lesion, but not fibroadenoma. Recently there is new evidence that shows distinct clonality in the epithelial and stromal components of phyllodes tumour, implying that the epithelial component may also be neoplastic.44 To date, clonality studies have also provided evidence of a possible link between fibroadenoma and phyllodes tumours. In a very interesting clonality study of 45 fibroadenomas, it was found that while most of the fibroadenomas were polyclonal, two possessed monoclonal stromal component, while the histological correlate of one case showed distinct phyllodes tumour-like features in part of the lesion and the other case showed complex fibroadenoma morphology.47 In addition, there is strong evidence that fibroadenomas that are monoclonal may recur as phyllodes tumour, which demonstrates the same pattern of allelic inactivation,48,indicating that some ‘fibroadenomas’ are neoplastic at the outset and may behave more like a phyllodes tumour, resulting in recurrence with the same allelic inactivation pattern. Evidence of stromal progression has also been obtained in a PCR-based study,46 which showed that while the stroma of fibroadenoma and phyllodes tumours were polyclonal and monoclonal, respectively, foci of phyllodes-like stromal expansion within the fibroadenomas were monoclonal. These data are early evidence to suggest that an ‘intermediate lesion’ exists between fibroadenoma
ARTICLE IN PRESS Recent advances in the pathology of fibroepithelial tumours of the breast and phyllodes tumour, occurring as foci of phyllodal stromal pattern within an otherwise unremarkable fibroadenoma. Clonality studies are supportive of this postulation. Lastly, a discussion of fibroepithelial lesions would be incomplete without mentioning the concept of epithelial–stromal interaction. In a pioneer study, it has been shown that in fibroepithelial lesions, mitoses of the stromal cell tend to occur close to the epithelial element, suggesting that stromal growth is dependent on the epithelium.49 The finding of distinct molecular alterations in the epithelial and stromal components in phyllodes tumour,44 as well as the demonstration of a correlation between epithelial hormonal receptor status and the grade of the stromal component,32 have also lent weight to the epithelial contribution in the pathogenesis of phyllodes tumour. Recently an association between stromal beta-catenin with epithelial Wnt5a expression has been reported 50 and it is believed that in phyllodes tumour, the progression to malignancy results from stromal independence from the epithelium. This concept may represent a major step in our understanding of this group of biphasic lesions and warrants further detailed studies.
Practice points
Complex fibroadenomas show at least one of the following histological features: sclerosing adenosis, papillary apocrine metaplasia, cysts and epithelial calcifications. They have a slightly higher relative risk for cancer development compared with conventional fibroadenomas Phyllodes tumours are distinguished from fibroadenomas by their characteristic leaflike pattern accompanied by stromal hypercellularity Phyllodes tumours are graded into benign, borderline and malignant categories based on a constellation of histological changes that include stromal cellularity, mitotic count, stromal cytological atypia, stromal overgrowth and the nature of the margins (pushing versus permeative) All phyllodes tumours may recur and those of borderline or frank malignancy have a potential for metastases, with the latter having a higher metastastic potential Prediction of recurrence or metastasis based on histological parameters is still controversial and some authors have concluded that complete surgical excision is of
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key importance in the management of phyllodes tumours Biological markers do not, as yet, play an established role in determining the behaviour of phyllodes tumours; although studies on p53, proliferation markers, angiogenesis and CD117 in these tumours have been and are being carried out Future research in these biphasic tumours includes focusing on interactions between the epithelium and stroma, interrogating their molecular relationship and providing further insight into the pathogenesis of these lesions
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