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EUS-guided FNA for the diagnosis of GI stromal cell tumors: sensitivity and cytologic yield
ORIGINAL ARTICLE: Clinical Endoscopy
EUS-guided FNA for the diagnosis of GI stromal cell tumors: sensitivity and cytologic yield Paul S. Sepe, MD, Bhavani Moparty, MD, Martha B. Pitman, MD, John R. Saltzman, MD, William R. Brugge, MD Boston, Massachusetts, Dallas, Texas, USA
Background: EUS-guided FNA has been well documented to aid in the diagnosis of subepithelial lesions by providing cytologic material. Studies to date evaluating the sensitivity of EUS-FNA for the diagnosis of GI stromal cell tumors (GIST) have been small, and few have relied on surgical histologic diagnosis as the reference standard. Objective: Our purpose was to determine the diagnostic yield and sensitivity of EUS-FNA for the diagnosis of GIST and to identify EUS features of GIST that are predictive of the ability to obtain adequate tissue by EUS-FNA. Design: All patients with histologically confirmed, c-kit–positive GIST who underwent EUS-FNA from 1998 to 2006 were reviewed. EUS images were examined for mass size, shape, location, wall layer, heterogeneity, echogenicity, cystic spaces, lobulation, ulceration, and central umbilication. Needle gauge, number of needle passes, and presence of a cytologist during the EUS-FNA were recorded. Results: A total of 37 patients (29 with diagnostic FNA cytology; 8 with nondiagnostic cytology) met the inclusion criteria. The diagnostic yield and sensitivity of EUS-FNA cytology for the diagnosis of GIST was 78.4% (29/ 37). The sensitivity was 84.4% (27/32) for GISTs located in the stomach, but poor for lesions located in the duodenum because none of these tumors yielded diagnostic cytology (n Z 3). An increase in size up to 10 cm, round/oval shape, and identification of the origin of GIST within a specific sonographic wall layer were statistically significant in their ability to predict adequate tissue yield. Conclusions: The sensitivity of EUS-FNA cytology for the diagnosis of GIST is 78.4% and is influenced by size, location, shape, and layer of origin. (Gastrointest Endosc 2009;70:254-61.)
Copyright ª 2009 by the American Society for Gastrointestinal Endoscopy 0016-5107/$36.00 doi:10.1016/j.gie.2008.11.038
reasons and are characterized by a bulging of the GI wall with intact, normal, overlying mucosa (Fig. 1A). EUS allows both identification of tumor characteristics (Fig. 1B) and collection of tissue for diagnosis by EUSguided FNA.6-8 Studies to date evaluating the diagnostic yield and sensitivity of EUS-FNA cytology for the diagnosis of GIST have been small, and few have relied on surgical histologic examination as the reference standard.9-18 In addition, several of these studies took place before the use of c-kit (CD117) staining for the diagnosis of GIST. These limitations precluded the ability to study a pure GIST population because many of these tumors were likely leiomyomas or leiomyosarcomas. The purpose of this study was to determine the diagnostic yield and sensitivity of EUS-FNA cytologic study for the diagnosis of GIST. Given that sensitivity relies on the ability to obtain adequate tissue, we also wanted to identify EUS features of GIST that are predictive of the
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GI stromal cell tumors (GISTs) are mesenchymal tumors thought to originate from the interstitial cells of Cajal, which regulate GI motility.1-5 Recently, immunohistochemical staining for the tyrosine kinase protein, c-kit (CD117), has been shown to be present in approximately 95% of these tumors, thus allowing differentiation from other mesenchymal spindle-cell neoplasms.2,3 GISTs are frequently discovered on endoscopy performed for other Abbreviations: BWH, Brigham and Women’s Hospital; GIST, GI stromal cell tumors; IHC, immunohistochemical; MGH, Massachusetts General Hospital. DISCLOSURE: The following author disclosed financial relationships relevant to this publication: W. Brugge received an educational grant from Pentax Corporation. All other authors disclosed no financial relationships relevant to this publication.
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ability to obtain adequate tissue by EUS-FNA. To our knowledge, this is the largest well-defined patient cohort used to assess the role of EUS-FNA cytologic examination for the diagnosis of GIST.
EUS-FNA for diagnosis of GI stromal cell tumors
Capsule Summary What is already known on this topic d
METHODS
Determining the nature of GI stromal cell tumors (GISTs), frequent endoscopic coincidental findings, is difficult because current criteria lack consistency in predicting their malignancy risk.
In this retrospective study, the combined Massachusetts General Hospital (MGH) and Brigham and Women’s Hospital (BWH) pathology database was searched for all patients presenting between January 1998 and May 2006 with surgically resected, histologically confirmed, c-kit– positive GISTs. Computerized medical records were reviewed for all patients to determine those who also underwent EUS-guided FNA before surgical removal. Those patients with primary GISTs located in the esophagus, stomach, small intestine, and rectum were included (Table 1). Patients carrying a known diagnosis of GIST at the time of the EUS-guided FNA were excluded (ie, diagnosis previously made at an outside institution, those with secondary tumors, or documented metastatic GIST). In those cases where serial EUS was performed, only the initial examination was included. Records were further reviewed to stratify patients with either diagnostic or nondiagnostic cytology specimens by EUS-guided FNA. Cytology specimens were prepared as direct smears or a thin prep (Hologic/Cytyc, Marlborough, Mass) with routine Papanicolaou staining. Diagnostic cytology by FNA was primarily defined as spindle cells on smear (Fig. 1C). Because up to 20% to 30% of GISTs demonstrate epithelioid differentiation, this cytologic finding was considered diagnostic if present on the smear and the primary cytologist believed that GIST was the most likely diagnosis at the time of the final report. The results of c-kit staining on cell blocks were also recorded (if available) (Fig. 1D), although a positive c-kit stain was not necessary for a cytologic sample to be considered diagnostic. All EUS examinations were performed by 1 of 4 experienced endosonographers, 2 respectively at each institution. All patients underwent standard EGD and complete examination with a curvilinear-array echoendoscope (Pentax FG-36UX, Pentax Medical, Montvale, NJ; Olympus GF-UC140P-AL5, Olympus GF-UCT140-AL5, Olympus America, Center Valley, Pa). FNA was performed by making 1 to 7 passes with a 19-, 22-, or 25-gauge needle, at the discretion of the endosonographer. EUS images were reviewed by a single endosonographer for mass size, shape, location, wall layer, internal pattern, echogenicity, presence of cystic spaces, lobulation, ulceration, and central umbilication. Needle gauge, number of needle passes, and presence/absence of a cytologist on site during the procedure were also recorded. Data unable to be obtained through review of the primary images were extracted from the original endoscopy report. In evaluating the EUS mass characteristics, some parameters could
Review of the pathology database yielded 460 patients with surgically resected, histologically confirmed, c-kit– positive GISTs. Of these, 37 patients met inclusion criteria. GISTs were located in the stomach in 32 patients, the duodenum in 3 patients, the esophagus in 1 patient, and the rectum in 1 patient. There were 29 patients with diagnostic FNA cytologic findings (group A), and 8 patients with nondiagnostic cytologic findings (group B). A total of 44.8% (13/29) of patients in group A were male versus 62.5% (5/8) in group B (P Z .45). Mean age was 67.2 (14.9) years in group A versus 60.8 (11.6) years in group B (P Z .27). Diagnostic FNA cytology samples were characterized by spindle cells in 25 specimens,
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What this study adds to our knowledge d
The sensitivity of EUS-FNA cytology for the diagnosis of GIST was 78.4% and was influenced by size, location, shape, and layer of origin in 37 patients with histologically confirmed tumors.
not be evaluated because of insufficient image quality or reporting; this resulted in some disparities in data points (n values). Finally, GIST risk stratification of malignancy (high, intermediate, low) was recorded from surgical histology reports and defined as per current standards set forth by Fletcher et al.19
Statistics The Fisher exact test was used to analyze categorical data with 2 2 contingency tables. The 2-tailed t test was used to measure the statistical difference in means for tumor size and patient age between the 2 groups. Quantitative data are summarized by the mean and SD presented as ‘‘mean (SD).’’ It is recognized that there was multiple testing of outcome data arising from individual patients. It is noted that correction by the Bonferroni method would not have removed statistical significance from any of the main findings involving comparisons of sensitivity and anatomic differences between the groups of those with diagnostic and nondiagnostic cytologic findings. The P values for the other analyses are secondary and should be taken as descriptive only, so all P values are presented uncorrected for multiple testing.
RESULTS
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Figure 1. A, EGD image of a GIST, showing a gastric mass with smooth, intact, normal overlying mucosa (arrow). B, EUS image of a GIST, showing a round, hypoechoic mass located in the gastric wall (arrow). C, Cytologjc specimen from a GISTrevealing spindle cells on smear (arrow) (Papanicolaou staining, orig. mag. 600). D, Cell block specimen from a GIST revealing brown staining, positive for c-kit (CD 117 [c-kit] immunoperoxidase stain, orig. mag. 200).
spindle/epithelioid mixture in 2 specimens, and epithelioid cells in 2 specimens. A cell block was made in addition to a cytology smear in 13 of 37 (35.1%) patients and was positive for c-kit in only 6 of those 13 samples. Eleven cell blocks were made in group A patients, whereas only 2 cell blocks were made in group B. All 8 nondiagnostic cytology specimens were characterized by scant or acellular material. The diagnostic yield and sensitivity of EUS-FNA for the diagnosis of GIST was 78.4% (29/37). The sensitivity was 84.4% (27/32) for GISTs located in the stomach but poor for those lesions located in the duodenum because none of these tumors yielded diagnostic cytologic findings (n Z 3). When stratified by size, the sensitivity for tumors with size !2 cm, 2 to 5 cm, and 5 to 10 cm was 80%, 87.5%, and 100%, respectively, whereas none of the tumors O10 cm were able to be diagnosed (Table 2).
Anatomic characteristics of GIST as noted by EUS may be an important determinant in predicting cytologic yield from EUS-FNA. Tumors were located in the stomach in 27 of 29 (93.1%) patients in group A and 5 of 8 (62.5%) patients in group B (Table 3), whereas location in the duodenum occurred in 3 of 8 (37.5%) patients in group B but in 0 of 29 (0%) patients in group A. GISTs were significantly larger in the nondiagnostic group (group B), with a mean size of 78.1 (51.7) mm compared with 34.9 (16.2) mm in group A. When stratified by size, tumors O10 cm were present in 0 of 28 (0%) patients in group A compared with 4 of 8 (50%) patients in group B. Shape was also a statistically significant predictor with round/oval shape present in 26 of 27 (96.3%) tumors in group A but in only 2 of 7 (28.6%) in group B. Identification of the origin of a GIST within a specific sonographic wall layer appeared to be the
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TABLE 1. Study inclusion/exclusion criteria Inclusion criteria
be noted that when a cytologist was present, diagnostic cytology was obtained from 7 of 7 (100%) patients.
Exclusion criteria
Surgically removed, histologically confirmed, c-kit–positive GIST
Previous diagnosis of GIST at time of EUS
EUS-guided FNA before surgery
Prior diagnosis at outside institution
Initial EUS examination performed at one of the study institutions
Secondary tumors
Location in esophagus, stomach, small intestine, or rectum
Documented metastatic GIST
DISCUSSION
best predictor of cytologic yield because 28 of 28 (100%) tumors in group A were located in either the third or fourth sonographic layer, whereas only 1 of 6 (16.7%) tumors in group B was located in a specific layer (Fig. 2). Locale within a specific wall layer was unclear in the other 5 GISTs in this group. There was no statistical significance in the characteristics of echogenicitiy (P Z 1.0), echogenic foci (P Z 1.0), internal pattern (P Z 1.0), cystic spaces (P Z 1.0), lobulation (P Z .65), ulceration (P Z .31), umbilication (P Z .56), needle gauge (P Z .57), or number of needle passes (P Z 1.0) in the patients (group A vs group B). There was a trend (P Z .22) toward intermediate/high histologic risk stratification in the nondiagnostic group, with 5 of 8 (62.5%) meeting these criteria in group B compared with 9 of 29 (31.0 %) in group A. However, this did not meet statistical significance. Although the presence of a cytologist was rare and thus did not meet statistical significance in predicting cytologic yield (P Z .31), it should
GISTs are the most commonly identified intramural, subepithelial mass in the upper GI tract, accounting for approximately 5000 to 6000 new cases each year.6 These masses are frequently found on endoscopy performed for other reasons, but patients may also present with abdominal pain, bleeding, or symptoms of mass effect. Approximately 20% to 25% of gastric and 40% to 50% of small-intestinal GISTs are clinically malignant,3 but it is well recognized that all GISTs have some degree of malignant potential. Even small localized GISTs may demonstrate malignant features on histologic examination or biologic behavior. Determining the biologic nature of GIST at initial diagnosis has proven elusive because current histopathologic criteria lack consistency in predicting malignant risk.20 This manifests the importance of making the diagnosis of GIST on initial evaluation. Unfortunately, GIST location in the muscularis propria, beneath the submucosa, precludes reliable diagnosis by endoscopic forceps biopsy or EMR because of either lack of adequate sampling from deeper layers or risk of perforation.6,7 EUS-guided FNA has been well documented as providing cytologic material for the diagnosis of malignancy, but large studies assessing its utility have mainly looked at its use in sampling lymph nodes, the pancreas, and extraintestinal masses.17,18,21-25 Studies assessing its role in the diagnosis of GIST have been small, and few have relied on surgical histologic diagnosis as the reference standard.9-14,16 In most studies, details remain vague as to the presence or absence of surgical confirmation and whether nondiagnostic samples were included in the final analysis. Ando et al10 retrospectively examined 49 patients with submucosal tumors originating from the fourth sonographic layer. In 4 patients, specimens were inadequate for histopathologic diagnosis, giving a diagnostic yield of 91.8% (45/49). Twenty-two patients were lost to followup. Twenty-three patients underwent surgical resection, with positive c-kit staining in 20 of 23 patients. EUS-FNA was diagnostic in 19 of these 20 confirmed GISTs, for a calculated sensitivity of 95%. However, it is unclear whether the 4 nondiagnostic specimens were true GISTs, which would have negatively affected the sensitivity. Vander Noot et al16 studied 62 intramural and extramural masses by EUS-FNA. Of the 18 GISTs, 17 of 18 samples were of adequate tissue, resulting in a diagnostic yield of 94.4%. It is unclear whether GIST histologic features were confirmed by surgical resection. Okubo et al14 examined 18 patients with GIST undergoing both EUS-FNA and surgical resection and calculated a diagnostic yield and sensitivity of 78.0% (14/18).
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Extraintestinal GIST Initial EUS performed at outside institution
TABLE 2. Sensitivity of EUS-FNA for the diagnosis of GIST Sensitivity of EUS-FNA (%) Overall
29/37 (78.4)
Location in stomach
27/32 (84.4)*
Location in duodenum
0/3 (0)
Size !2 cm
4/5 (80)
Size 2-5 cm
21/24 (87.5)
Size 5-10 cm
4/4 (100)
Size O10 cm
0/4 (0)y
*P value .009 for the difference of sensitivity between stomach and duodenum. yP value .001 for the difference of sensitivity between size !10 cm and O10 cm.
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TABLE 3. EUS imaging features and association with cytologic yield
Imaging features
Group A: diagnostic cytology (%)
Group B: nondiagnostic cytology (%)
P value
27/29 (93.1)
5/8 (62.5)
.06
3/8 (37.5)
.007 .0003 (95% CI, 21.1-65.4)
Anatomic Location in stomach Location in duodenum
0/29 (0)
Mean size (mm)
34.9 (16.2)
78.1 (51.7)
26/27 (96.3)
2/7 (28.6)
.0004
1/27 (3.7)
5/7 (71.4)
.0004
28/28 (100)
1/6 (16.7)
!.0001
0
5/6 (83.3)
!.0001
Round/oval shape Irregular shape Third/fourth sonographic wall layer Unclear sonographic wall layer Biologic Hyperechoic echogenicity
2/27 (7.4)
0/7 (0)
1.0
Echogenic foci
19/26 (73.0)
4/6 (66.7)
1.0
Heterogenous internal patern
25/28 (89.3)
6.7 (85.7)
1.0
Cystic spaces
16/28 (57.1)
4/6 (66.7)
1.0
Lobulation
9/26 (34.6)
3/6 (50.0)
.65
Ulceration
6/27(22.2)
3/6 (50.0)
.31
Umbilication
5/26 (19.2)
0/6 (0)
.56
Intermediate-/high-risk histologic features
9/29 (31.0)
5/8 (62.5)
.22
Presence of cytologist
7/29 (24.1)
0/8 (0)
.31
19-gauge needle
4/29 (13.8)
0/7 (0)
.57
Procedural
%2 Needle passes
19/26 (73.1)
5/6 (83.3)
1.0
O2 Needle passes
7/26 (26.9)
1/6 (16.7)
1.0
Some parameters could not be evaluated because of insufficient image quality or reporting; this resulted in occasional disparities in data points (n values).
Recently, Akahoshi et al9 studied 53 subepithelial gastric tumors. Diagnostic specimens were obtained in 42/51 (82%) patients. Of these 42 patients, there were a total of 31 GISTs, 24 of which were verified by surgical histologic examination. An abstract by Hoda et al, discussed in a recent review,26 represents the largest study to date examining the diagnostic yield of EUS-FNA for the diagnosis of GIST. A total of 120 patients with subepithelial lesions were retrospectively reviewed. EUS-FNA was diagnostic for GIST in 27.5% and suspicious (spindle cells) in 12.5%. FNA also revealed leiomyoma in 23.3%, neural tumors in 2.4%, and nondiagnostic cytologic findings in 33.3%. However, the cytologic diagnosis was not verified by surgical histologic findings. EUS-guided FNA sampling has become standard practice in the evaluation of GIST. However, as mentioned above, the majority of information regarding its utility has been extrapolated from small studies using reference
standards that were not well defined. This study aimed to avoid these shortcomings by studying a well-defined patient cohort based on the evidence of surgical histologic study. Our main purpose was to determine the diagnostic yield and sensitivity of EUS-guided FNA for the diagnosis of GIST. Because FNA is limited by low cellularity of specimens and poor cytologic yield in up to 33.3% of samples, its sensitivity relies heavily on the ability to obtain adequate tissue. Considering this, the secondary aim of this study was to determine predictors of cytologic yield by using features from the EUS examination. In this study, overall diagnostic tissue yield of EUS-FNA was 78.4%. Because we used a patient cohort defined by the results of surgical histologic study, the sensitivity was also 78.4%. Diagnostic cytology was defined as a descriptive diagnosis of spindle or epithelioid cells on smear rather than an immunohistochemical (IHC) diagnosis of positive c-kit. Cell block availability was limited at the participating institutions during the study period. However,
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this deficiency probably had a minor impact because the study population was composed of surgically removed, histologically confirmed, c-kit–positive GISTs. In addition, cell block for IHC staining requires adequate sampling, and because of this, endosonographers are frequently faced with ‘‘spindle cells’’ or ‘‘epithelioid cells’’ on smear rather than an IHC diagnosis. Thus, this descriptive diagnosis most likely reflects the performance of EUS-FNA in the general population. This low threshold of spindle or epithelioid cells on smear does, however, provide a ‘‘best case scenario,’’ likely overestimating sensitivity and decreasing specificity compared with an IHC diagnosis. Considering this, a sensitivity of 78.4% is still well below that of other published data. The most likely reason for this difference was the presence of an on-site cytopathologist to immediately review adequacy of samples in both studies quoting sensitivity O90%.12,16 In our study, a cytopathologist was present in only 18.9% (7/37) of EUS-FNAs. However, adequate tissue was obtained 100%
(7/7) of the time when a cytopathologist was available. Another reason for lower diagnostic yield and sensitivity in our study is that it likely more accurately reflects tissue yield as it is obtained in everyday practice. The fact that diagnostic yield did not differ significantly between the 2 different institutions in this study (77.8% MGH vs 80% BWH) supports this. In our study, the sensitivity of EUS-FNA cytologic examination for a GIST located in the stomach was 84.4% (27/ 32), whereas 0 of 3 tumors located in the duodenum yielded diagnostic cytologic findings. This underscores the importance of accessibility of the GIST because tumors located within the stomach are clearly more amenable to sampling than are those located in the small intestine. The sensitivity was also increased with increased tumor size, up to a threshold of 10 cm. The sensitivity was 80%, 87.5%, 100%, and 0% for tumors with size !2 cm, 2 to 5 cm, 5 to 10 cm, and O10 cm, respectively. These findings suggest that sensitivity correlated with tumor size for GISTs smaller than 10 cm. It was surprising that large tumors greater than 10 cm did not yield diagnostic cytologic material. One possible mechanism is that larger tumors are more prone to necrosis, which could potentially play a role in making FNA of these lesions more difficult. A review of the surgical histologic diagnoses of the 4 tumors greater than 10 cm revealed that 3 of 4 were noted to have areas of necrosis or patchy hemorrhage throughout. The fourth tumor had a large cystic component. Although it is unclear exactly how much these factors contributed, they may have had a role in determining the cytologic yield by interfering with adequate sampling. Of note, the study of Akahoshi et al al9 so found that tumor size correlated with diagnostic yield and sensitivity, although the authors did not find a threshold effect as described here. Our findings suggest that the sensitivity and diagnostic yield of EUS-FNA for the diagnosis of GIST compare favorably with other well-accepted indications of this procedure, such as sampling pancreatic lesions and lymph nodes. More conventional sampling techniques, such as forceps biopsy or EMR, are limited in their clinical utility, given the difficulty of sampling lesions in a subepithelial location and the increased risk for perforation, respectively. In addition, a clear role for EUS-guided Tru-cut biopsy has yet to be defined, given inconsistent results in its ability to provide adequate tissue yield. More studies will have to be done to further elucidate a well-defined role for these alternative sampling techniques. However, at present, EUS-FNA should be considered the procedure of choice to secure a tissue diagnosis of GIST. In examining features of GIST that are predictive of the ability to obtain adequate tissue yield, increasing size up to 10 cm, round/oval shape, and location in a specific sonographic wall layer were statistically significant in their ability to predict adequate tissue yield. Duodenal location, size O10 cm, irregular shape, and unclear sonographic wall
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Figure 2. A, EUS image of a GIST representative of the diagnostic cytology group (group A), showing a small round GIST located within a specific sonographic wall layer. B, EUS image of a GIST representative of the nondiagnostic cytology group (group B), showing a large irregular GIST located in an unclear sonographic wall layer (arrow).
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layer were significantly associated with inadequate tissue yield and thus with nondiagnostic cytology samples. Statistical significance was demonstrated for each anatomic factor studied, whereas none of the biologic or procedural factors were of significance. These findings demonstrate that EUS-guided FNA sampling may not necessarily be dependent on the histologic composition of the tumor. There was a trend toward intermediate/high risk histologic findings in the nondiagnostic group. However, this was likely because size represents 1 of the 2 criteria used in stratifying the malignant risk for GIST (mitotic count being the other), as described by Fletcher et al.19 The current study was underpowered to adequately assess procedural factors, such as needle gauge, number of needle passes, and the presence of a cytologist. Although it may be intuitive that more passes or use of a larger-bore needle would provide more tissue, this study does not demonstrate a clear association. It should be noted that only 1 to 2 needle passes were made in the majority of patients (73.1% in group A vs 83.3% in group B). However, the number of passes was not significantly different between the 2 groups (P Z 1.0). As is standard practice, this decision was made at the discretion of the individual endosongrapher and was based on a real-time assessment of presumed tissue adequacy and the risk/benefit ratio of further passes in each case. Despite lacking statistical significance, it is clear that when a cytologist was present, adequate tissue was obtained 100% (7/7) of the time compared with 73% (22/30) when a cytologist was not present. This trend merits attention because the presence of a cytologist could represent the added measure necessary to bridge the gap between a diagnostic yield of 78.4% as in this study and one approaching 100%. Given the predictive features described above, a tailored approach to EUS-FNA could be envisioned where the endosonographer uses an on-site cytopathologist when encountering a GIST tumor characterized by anatomic features predictive of inadequate tissue yield. Although not yet prospectively studied, this approach would most likely increase the yield while limiting the unnecessary overuse of a valuable resource. This study has several important strengths. The patient cohort was well defined and histologically based and, to our knowledge, represents the largest such cohort to date used to assess the role of EUS-guided FNA cytologic findings for the diagnosis of GIST. Although we are unable to calculate specificity, positive predictive value, negative predictive value, or diagnostic accuracy, our approach allowed an accurate calculation of both sensitivity and diagnostic yield. The calculation of only sensitivity and diagnostic yield does provide a statistical weakness that should be interpreted with caution. Nonetheless, we feel that these results significantly build on the very sparse and limited data available in this field. An additional strength of this study is that it included patients from 2 different medical centers, helping to protect against institutional bias and further increasing its generalizability.
There are also several weaknesses. Only 37 patients of the initial 460 collected from the pathology database fulfilled inclusion criteria and had EUS-guided FNA before surgical removal of the GIST. The majority of the other 423 did not undergo EUS-guided FNA because they either proceeded directly to surgical resection from radiologic imaging or their tumors were discovered on postmortem examination. Thus, we are studying a very small, select subpopulation of patients. This selection bias should be recognized, but likely only had a minimal effect on our results because the purpose of our study was to examine this select subpopulation, a group of patients where diagnosis and further management could possibly be aided by EUS-guided FNA. In addition, although this study is very large compared with other GIST or EUS studies, the patient cohort is rather small. This limited our ability to provide statistical power to detect significant differences, especially considering the number of factors that were studied. This was most evident when procedural factors were assessed, in which variations in needle gauge and number of passes and the presence/absence of a cytologist were too few to detect statistical significance. This also limited our ability to perform multivariate analysis. Given that only univariate analysis was performed, conclusions should be interpreted with caution. Although we are not able to determine the independence of particular variables, our results suggest that anatomic factors play a more important role in adequate sampling than do biologic factors. Considering this, we feel that univariate analysis is able to provide us with some basic conclusions in an area that has a sparsity of available data in the current literature. In conclusion, the sensitivity of EUS-FNA for the diagnosis of GIST is 78.4%, and it is influenced by size, location, shape, and layer of origin.
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ACKNOWLEDGMENTS We thank Shiva Gautam, PhD, for his help in reviewing the statistics in this article.
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6. Hwang JH, Kimmey MB. The incidental upper gastrointestinal subepithelial mass. Gastroenterology 2004;126:301-7. 7. Hwang JH, Rulyak SD, Kimmey MB. American Gastroenterological Association Institute technical review on the management of gastric subepithelial masses. Gastroenterology 2006;130:2217-28. 8. Al-Haddad M, Wallace MB, Woodward TA, et al. The safety of fineneedle aspiration guided by endoscopic ultrasound: a prospective study. Endoscopy 2008;40:204-8. 9. Akahoshi K, Sumida Y, Matsui N, et al. Preoperative diagnosis of gastrointestinal stromal tumor by endoscopic ultrasound-guided fine needle aspiration. World J Gastroenterol 2007;13:2077-82. 10. Ando N, Goto H, Niwa Y, et al. The diagnosis of GI stromal tumors with EUS-guided fine needle aspiration with immunohistochemical analysis. Gastrointest Endosc 2002;55:37-43. 11. Arantes V, Logrono R, Faruqi S, et al. Endoscopic sonographically guided fine-needle aspiration yield in submucosal tumors of the gastrointestinal tract. J Ultrasound Med 2004;23:1141-50. 12. Chen VK, Eloubeidi MA. Endoscopic ultrasound-guided fine-needle aspiration of intramural and extraintestinal mass lesions: diagnostic accuracy, complication assessment, and impact on management. Endoscopy 2005;37:984-9. 13. Gu M, Ghafari S, Nguyen PT, et al. Cytologic diagnosis of gastrointestinal stromal tumors of the stomach by endoscopic ultrasound-guided fine-needle aspiration biopsy: cytomorphologic and immunohistochemical study of 12 cases. Diagn Cytopathol 2001;25:343-50. 14. Okubo K, Yamao K, Nakamura T, et al. Endoscopic ultrasound guided fine-needle aspiration biopsy for the diagnosis of gastrointestinal stromal tumors in the stomach. J Gastroenterol 2004;39:747-53. 15. Polkowski M. Endoscopic ultrasound and endoscopic ultrasoundguided fine-needle biopsy for the diagnosis of malignant submucosal tumors. Endoscopy 2005;37:635-45. 16. Vander Noot MR III, Eloubeidi MA, Chen VK, et al. Diagnosis of gastrointestinal tract lesions by endoscopic ultrasound-guided fine-needle aspiration biopsy. Cancer 2004;102:157-63. 17. Wiersema MJ, Vilmann P, Giovannini M, et al. Endosonography-guided fine-needle aspiration biopsy: diagnostic accuracy and complication assessment. Gastroenterology 1997;112:1087-95. 18. Williams DB, Sahai AV, Aabakken L, et al. Endoscopic ultrasound guided fine needle aspiration biopsy: a large single centre experience. Gut 1999;44:720-6.
19. Fletcher CD, Berman JJ, Corless C, et al. Diagnosis of gastrointestinal stromal tumors: a consensus approach. Hum Pathol 2002;33:459-65. 20. Nowain A, Bhakta H, Pais S, et al. Gastrointestinal stromal tumors: clinical profile, pathogenesis, treatment strategies and prognosis. J Gastroenterol Hepatol 2005;20:818-24. 21. Chhieng DC, Jhala D, Jhala N, et al. Endoscopic ultrasound guided fine-needle aspiration biopsy: a study of 103 cases. Cancer 2002;96: 232-9. 22. Eloubeidi MA, Jhala D, Chhieng DC, et al. Yield of endoscopic ultrasound guided fine-needle aspiration biopsy in patients with suspected pancreatic carcinoma. Cancer 2003;99:285-92. 23. Giovannini M, Seitz JF, Monges G, et al. Fine-needle aspiration cytology guided by endoscopic ultrasonography: results in 141 patients. Endoscopy 1995;27:171-7. 24. Shin HJ, Lahoti S, Sneige N. Endoscopic ultrasound guided fine-needle aspiration in 179 cases: the M.D. Anderson Cancer Center experience. Cancer 2002;96:174-80. 25. Wiersema MJ, Wiersema LM, Khusro Q, et al. Combined endosonography and fine-needle aspiration cytology in the evaluation of gastrointestinal lesions. Gastrointest Endosc 1994;40:199-206. 26. Rodriguez SA, Faigel DO. Endoscopic diagnosis of gastrointestinal tromal cell tumors. Curr Opin Gastroenterol 2007;23:539-43.
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Received July 16, 2008. Accepted November 20, 2008. Current affiliations: Division of Gastroenterology, Department of Medicine, Beth Israel Deaconess Medical Center (P.S.S.), Department of Pathology (M.B.P.) and Gastrointestinal Unit, Department of Medicine (W.R.B.), Massachusetts General Hospital, Division of Gastroenterology, Department of Medicine, Brigham and Women’s Hospital (J.R.S.), Boston, Massachusetts, Texas Digestive Disease Consultants, Baylor University Medical Center (B.M.), Dallas, Texas, USA. Presented at Digestive Diseases Week, May 21, 2007, Washington, DC (Gastrointest Endosc 2007;65:AB205). Reprint requests: William R. Brugge, MD, Gastrointestinal Unit, Massachusetts General Hospital, 55 Fruit St, Boston, MA 02114. If you want to chat with an author of this article, you may contact him at [email protected].
EUS-guided FNA for the diagnosis of GI stromal cell tumors: sensitivity and cytologic yield Paul S. Sepe, MD, Bhavani Moparty, MD, Martha B. Pitman, MD, John R. Saltzman, MD, William R. Brugge, MD Boston, Massachusetts, Dallas, Texas, USA
Background: EUS-guided FNA has been well documented to aid in the diagnosis of subepithelial lesions by providing cytologic material. Studies to date evaluating the sensitivity of EUS-FNA for the diagnosis of GI stromal cell tumors (GIST) have been small, and few have relied on surgical histologic diagnosis as the reference standard. Objective: Our purpose was to determine the diagnostic yield and sensitivity of EUS-FNA for the diagnosis of GIST and to identify EUS features of GIST that are predictive of the ability to obtain adequate tissue by EUS-FNA. Design: All patients with histologically confirmed, c-kit–positive GIST who underwent EUS-FNA from 1998 to 2006 were reviewed. EUS images were examined for mass size, shape, location, wall layer, heterogeneity, echogenicity, cystic spaces, lobulation, ulceration, and central umbilication. Needle gauge, number of needle passes, and presence of a cytologist during the EUS-FNA were recorded. Results: A total of 37 patients (29 with diagnostic FNA cytology; 8 with nondiagnostic cytology) met the inclusion criteria. The diagnostic yield and sensitivity of EUS-FNA cytology for the diagnosis of GIST was 78.4% (29/ 37). The sensitivity was 84.4% (27/32) for GISTs located in the stomach, but poor for lesions located in the duodenum because none of these tumors yielded diagnostic cytology (n Z 3). An increase in size up to 10 cm, round/oval shape, and identification of the origin of GIST within a specific sonographic wall layer were statistically significant in their ability to predict adequate tissue yield. Conclusions: The sensitivity of EUS-FNA cytology for the diagnosis of GIST is 78.4% and is influenced by size, location, shape, and layer of origin. (Gastrointest Endosc 2009;70:254-61.)
Copyright ª 2009 by the American Society for Gastrointestinal Endoscopy 0016-5107/$36.00 doi:10.1016/j.gie.2008.11.038
reasons and are characterized by a bulging of the GI wall with intact, normal, overlying mucosa (Fig. 1A). EUS allows both identification of tumor characteristics (Fig. 1B) and collection of tissue for diagnosis by EUSguided FNA.6-8 Studies to date evaluating the diagnostic yield and sensitivity of EUS-FNA cytology for the diagnosis of GIST have been small, and few have relied on surgical histologic examination as the reference standard.9-18 In addition, several of these studies took place before the use of c-kit (CD117) staining for the diagnosis of GIST. These limitations precluded the ability to study a pure GIST population because many of these tumors were likely leiomyomas or leiomyosarcomas. The purpose of this study was to determine the diagnostic yield and sensitivity of EUS-FNA cytologic study for the diagnosis of GIST. Given that sensitivity relies on the ability to obtain adequate tissue, we also wanted to identify EUS features of GIST that are predictive of the
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GI stromal cell tumors (GISTs) are mesenchymal tumors thought to originate from the interstitial cells of Cajal, which regulate GI motility.1-5 Recently, immunohistochemical staining for the tyrosine kinase protein, c-kit (CD117), has been shown to be present in approximately 95% of these tumors, thus allowing differentiation from other mesenchymal spindle-cell neoplasms.2,3 GISTs are frequently discovered on endoscopy performed for other Abbreviations: BWH, Brigham and Women’s Hospital; GIST, GI stromal cell tumors; IHC, immunohistochemical; MGH, Massachusetts General Hospital. DISCLOSURE: The following author disclosed financial relationships relevant to this publication: W. Brugge received an educational grant from Pentax Corporation. All other authors disclosed no financial relationships relevant to this publication.
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ability to obtain adequate tissue by EUS-FNA. To our knowledge, this is the largest well-defined patient cohort used to assess the role of EUS-FNA cytologic examination for the diagnosis of GIST.
EUS-FNA for diagnosis of GI stromal cell tumors
Capsule Summary What is already known on this topic d
METHODS
Determining the nature of GI stromal cell tumors (GISTs), frequent endoscopic coincidental findings, is difficult because current criteria lack consistency in predicting their malignancy risk.
In this retrospective study, the combined Massachusetts General Hospital (MGH) and Brigham and Women’s Hospital (BWH) pathology database was searched for all patients presenting between January 1998 and May 2006 with surgically resected, histologically confirmed, c-kit– positive GISTs. Computerized medical records were reviewed for all patients to determine those who also underwent EUS-guided FNA before surgical removal. Those patients with primary GISTs located in the esophagus, stomach, small intestine, and rectum were included (Table 1). Patients carrying a known diagnosis of GIST at the time of the EUS-guided FNA were excluded (ie, diagnosis previously made at an outside institution, those with secondary tumors, or documented metastatic GIST). In those cases where serial EUS was performed, only the initial examination was included. Records were further reviewed to stratify patients with either diagnostic or nondiagnostic cytology specimens by EUS-guided FNA. Cytology specimens were prepared as direct smears or a thin prep (Hologic/Cytyc, Marlborough, Mass) with routine Papanicolaou staining. Diagnostic cytology by FNA was primarily defined as spindle cells on smear (Fig. 1C). Because up to 20% to 30% of GISTs demonstrate epithelioid differentiation, this cytologic finding was considered diagnostic if present on the smear and the primary cytologist believed that GIST was the most likely diagnosis at the time of the final report. The results of c-kit staining on cell blocks were also recorded (if available) (Fig. 1D), although a positive c-kit stain was not necessary for a cytologic sample to be considered diagnostic. All EUS examinations were performed by 1 of 4 experienced endosonographers, 2 respectively at each institution. All patients underwent standard EGD and complete examination with a curvilinear-array echoendoscope (Pentax FG-36UX, Pentax Medical, Montvale, NJ; Olympus GF-UC140P-AL5, Olympus GF-UCT140-AL5, Olympus America, Center Valley, Pa). FNA was performed by making 1 to 7 passes with a 19-, 22-, or 25-gauge needle, at the discretion of the endosonographer. EUS images were reviewed by a single endosonographer for mass size, shape, location, wall layer, internal pattern, echogenicity, presence of cystic spaces, lobulation, ulceration, and central umbilication. Needle gauge, number of needle passes, and presence/absence of a cytologist on site during the procedure were also recorded. Data unable to be obtained through review of the primary images were extracted from the original endoscopy report. In evaluating the EUS mass characteristics, some parameters could
Review of the pathology database yielded 460 patients with surgically resected, histologically confirmed, c-kit– positive GISTs. Of these, 37 patients met inclusion criteria. GISTs were located in the stomach in 32 patients, the duodenum in 3 patients, the esophagus in 1 patient, and the rectum in 1 patient. There were 29 patients with diagnostic FNA cytologic findings (group A), and 8 patients with nondiagnostic cytologic findings (group B). A total of 44.8% (13/29) of patients in group A were male versus 62.5% (5/8) in group B (P Z .45). Mean age was 67.2 (14.9) years in group A versus 60.8 (11.6) years in group B (P Z .27). Diagnostic FNA cytology samples were characterized by spindle cells in 25 specimens,
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What this study adds to our knowledge d
The sensitivity of EUS-FNA cytology for the diagnosis of GIST was 78.4% and was influenced by size, location, shape, and layer of origin in 37 patients with histologically confirmed tumors.
not be evaluated because of insufficient image quality or reporting; this resulted in some disparities in data points (n values). Finally, GIST risk stratification of malignancy (high, intermediate, low) was recorded from surgical histology reports and defined as per current standards set forth by Fletcher et al.19
Statistics The Fisher exact test was used to analyze categorical data with 2 2 contingency tables. The 2-tailed t test was used to measure the statistical difference in means for tumor size and patient age between the 2 groups. Quantitative data are summarized by the mean and SD presented as ‘‘mean (SD).’’ It is recognized that there was multiple testing of outcome data arising from individual patients. It is noted that correction by the Bonferroni method would not have removed statistical significance from any of the main findings involving comparisons of sensitivity and anatomic differences between the groups of those with diagnostic and nondiagnostic cytologic findings. The P values for the other analyses are secondary and should be taken as descriptive only, so all P values are presented uncorrected for multiple testing.
RESULTS
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Figure 1. A, EGD image of a GIST, showing a gastric mass with smooth, intact, normal overlying mucosa (arrow). B, EUS image of a GIST, showing a round, hypoechoic mass located in the gastric wall (arrow). C, Cytologjc specimen from a GISTrevealing spindle cells on smear (arrow) (Papanicolaou staining, orig. mag. 600). D, Cell block specimen from a GIST revealing brown staining, positive for c-kit (CD 117 [c-kit] immunoperoxidase stain, orig. mag. 200).
spindle/epithelioid mixture in 2 specimens, and epithelioid cells in 2 specimens. A cell block was made in addition to a cytology smear in 13 of 37 (35.1%) patients and was positive for c-kit in only 6 of those 13 samples. Eleven cell blocks were made in group A patients, whereas only 2 cell blocks were made in group B. All 8 nondiagnostic cytology specimens were characterized by scant or acellular material. The diagnostic yield and sensitivity of EUS-FNA for the diagnosis of GIST was 78.4% (29/37). The sensitivity was 84.4% (27/32) for GISTs located in the stomach but poor for those lesions located in the duodenum because none of these tumors yielded diagnostic cytologic findings (n Z 3). When stratified by size, the sensitivity for tumors with size !2 cm, 2 to 5 cm, and 5 to 10 cm was 80%, 87.5%, and 100%, respectively, whereas none of the tumors O10 cm were able to be diagnosed (Table 2).
Anatomic characteristics of GIST as noted by EUS may be an important determinant in predicting cytologic yield from EUS-FNA. Tumors were located in the stomach in 27 of 29 (93.1%) patients in group A and 5 of 8 (62.5%) patients in group B (Table 3), whereas location in the duodenum occurred in 3 of 8 (37.5%) patients in group B but in 0 of 29 (0%) patients in group A. GISTs were significantly larger in the nondiagnostic group (group B), with a mean size of 78.1 (51.7) mm compared with 34.9 (16.2) mm in group A. When stratified by size, tumors O10 cm were present in 0 of 28 (0%) patients in group A compared with 4 of 8 (50%) patients in group B. Shape was also a statistically significant predictor with round/oval shape present in 26 of 27 (96.3%) tumors in group A but in only 2 of 7 (28.6%) in group B. Identification of the origin of a GIST within a specific sonographic wall layer appeared to be the
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TABLE 1. Study inclusion/exclusion criteria Inclusion criteria
be noted that when a cytologist was present, diagnostic cytology was obtained from 7 of 7 (100%) patients.
Exclusion criteria
Surgically removed, histologically confirmed, c-kit–positive GIST
Previous diagnosis of GIST at time of EUS
EUS-guided FNA before surgery
Prior diagnosis at outside institution
Initial EUS examination performed at one of the study institutions
Secondary tumors
Location in esophagus, stomach, small intestine, or rectum
Documented metastatic GIST
DISCUSSION
best predictor of cytologic yield because 28 of 28 (100%) tumors in group A were located in either the third or fourth sonographic layer, whereas only 1 of 6 (16.7%) tumors in group B was located in a specific layer (Fig. 2). Locale within a specific wall layer was unclear in the other 5 GISTs in this group. There was no statistical significance in the characteristics of echogenicitiy (P Z 1.0), echogenic foci (P Z 1.0), internal pattern (P Z 1.0), cystic spaces (P Z 1.0), lobulation (P Z .65), ulceration (P Z .31), umbilication (P Z .56), needle gauge (P Z .57), or number of needle passes (P Z 1.0) in the patients (group A vs group B). There was a trend (P Z .22) toward intermediate/high histologic risk stratification in the nondiagnostic group, with 5 of 8 (62.5%) meeting these criteria in group B compared with 9 of 29 (31.0 %) in group A. However, this did not meet statistical significance. Although the presence of a cytologist was rare and thus did not meet statistical significance in predicting cytologic yield (P Z .31), it should
GISTs are the most commonly identified intramural, subepithelial mass in the upper GI tract, accounting for approximately 5000 to 6000 new cases each year.6 These masses are frequently found on endoscopy performed for other reasons, but patients may also present with abdominal pain, bleeding, or symptoms of mass effect. Approximately 20% to 25% of gastric and 40% to 50% of small-intestinal GISTs are clinically malignant,3 but it is well recognized that all GISTs have some degree of malignant potential. Even small localized GISTs may demonstrate malignant features on histologic examination or biologic behavior. Determining the biologic nature of GIST at initial diagnosis has proven elusive because current histopathologic criteria lack consistency in predicting malignant risk.20 This manifests the importance of making the diagnosis of GIST on initial evaluation. Unfortunately, GIST location in the muscularis propria, beneath the submucosa, precludes reliable diagnosis by endoscopic forceps biopsy or EMR because of either lack of adequate sampling from deeper layers or risk of perforation.6,7 EUS-guided FNA has been well documented as providing cytologic material for the diagnosis of malignancy, but large studies assessing its utility have mainly looked at its use in sampling lymph nodes, the pancreas, and extraintestinal masses.17,18,21-25 Studies assessing its role in the diagnosis of GIST have been small, and few have relied on surgical histologic diagnosis as the reference standard.9-14,16 In most studies, details remain vague as to the presence or absence of surgical confirmation and whether nondiagnostic samples were included in the final analysis. Ando et al10 retrospectively examined 49 patients with submucosal tumors originating from the fourth sonographic layer. In 4 patients, specimens were inadequate for histopathologic diagnosis, giving a diagnostic yield of 91.8% (45/49). Twenty-two patients were lost to followup. Twenty-three patients underwent surgical resection, with positive c-kit staining in 20 of 23 patients. EUS-FNA was diagnostic in 19 of these 20 confirmed GISTs, for a calculated sensitivity of 95%. However, it is unclear whether the 4 nondiagnostic specimens were true GISTs, which would have negatively affected the sensitivity. Vander Noot et al16 studied 62 intramural and extramural masses by EUS-FNA. Of the 18 GISTs, 17 of 18 samples were of adequate tissue, resulting in a diagnostic yield of 94.4%. It is unclear whether GIST histologic features were confirmed by surgical resection. Okubo et al14 examined 18 patients with GIST undergoing both EUS-FNA and surgical resection and calculated a diagnostic yield and sensitivity of 78.0% (14/18).
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Extraintestinal GIST Initial EUS performed at outside institution
TABLE 2. Sensitivity of EUS-FNA for the diagnosis of GIST Sensitivity of EUS-FNA (%) Overall
29/37 (78.4)
Location in stomach
27/32 (84.4)*
Location in duodenum
0/3 (0)
Size !2 cm
4/5 (80)
Size 2-5 cm
21/24 (87.5)
Size 5-10 cm
4/4 (100)
Size O10 cm
0/4 (0)y
*P value .009 for the difference of sensitivity between stomach and duodenum. yP value .001 for the difference of sensitivity between size !10 cm and O10 cm.
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TABLE 3. EUS imaging features and association with cytologic yield
Imaging features
Group A: diagnostic cytology (%)
Group B: nondiagnostic cytology (%)
P value
27/29 (93.1)
5/8 (62.5)
.06
3/8 (37.5)
.007 .0003 (95% CI, 21.1-65.4)
Anatomic Location in stomach Location in duodenum
0/29 (0)
Mean size (mm)
34.9 (16.2)
78.1 (51.7)
26/27 (96.3)
2/7 (28.6)
.0004
1/27 (3.7)
5/7 (71.4)
.0004
28/28 (100)
1/6 (16.7)
!.0001
0
5/6 (83.3)
!.0001
Round/oval shape Irregular shape Third/fourth sonographic wall layer Unclear sonographic wall layer Biologic Hyperechoic echogenicity
2/27 (7.4)
0/7 (0)
1.0
Echogenic foci
19/26 (73.0)
4/6 (66.7)
1.0
Heterogenous internal patern
25/28 (89.3)
6.7 (85.7)
1.0
Cystic spaces
16/28 (57.1)
4/6 (66.7)
1.0
Lobulation
9/26 (34.6)
3/6 (50.0)
.65
Ulceration
6/27(22.2)
3/6 (50.0)
.31
Umbilication
5/26 (19.2)
0/6 (0)
.56
Intermediate-/high-risk histologic features
9/29 (31.0)
5/8 (62.5)
.22
Presence of cytologist
7/29 (24.1)
0/8 (0)
.31
19-gauge needle
4/29 (13.8)
0/7 (0)
.57
Procedural
%2 Needle passes
19/26 (73.1)
5/6 (83.3)
1.0
O2 Needle passes
7/26 (26.9)
1/6 (16.7)
1.0
Some parameters could not be evaluated because of insufficient image quality or reporting; this resulted in occasional disparities in data points (n values).
Recently, Akahoshi et al9 studied 53 subepithelial gastric tumors. Diagnostic specimens were obtained in 42/51 (82%) patients. Of these 42 patients, there were a total of 31 GISTs, 24 of which were verified by surgical histologic examination. An abstract by Hoda et al, discussed in a recent review,26 represents the largest study to date examining the diagnostic yield of EUS-FNA for the diagnosis of GIST. A total of 120 patients with subepithelial lesions were retrospectively reviewed. EUS-FNA was diagnostic for GIST in 27.5% and suspicious (spindle cells) in 12.5%. FNA also revealed leiomyoma in 23.3%, neural tumors in 2.4%, and nondiagnostic cytologic findings in 33.3%. However, the cytologic diagnosis was not verified by surgical histologic findings. EUS-guided FNA sampling has become standard practice in the evaluation of GIST. However, as mentioned above, the majority of information regarding its utility has been extrapolated from small studies using reference
standards that were not well defined. This study aimed to avoid these shortcomings by studying a well-defined patient cohort based on the evidence of surgical histologic study. Our main purpose was to determine the diagnostic yield and sensitivity of EUS-guided FNA for the diagnosis of GIST. Because FNA is limited by low cellularity of specimens and poor cytologic yield in up to 33.3% of samples, its sensitivity relies heavily on the ability to obtain adequate tissue. Considering this, the secondary aim of this study was to determine predictors of cytologic yield by using features from the EUS examination. In this study, overall diagnostic tissue yield of EUS-FNA was 78.4%. Because we used a patient cohort defined by the results of surgical histologic study, the sensitivity was also 78.4%. Diagnostic cytology was defined as a descriptive diagnosis of spindle or epithelioid cells on smear rather than an immunohistochemical (IHC) diagnosis of positive c-kit. Cell block availability was limited at the participating institutions during the study period. However,
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this deficiency probably had a minor impact because the study population was composed of surgically removed, histologically confirmed, c-kit–positive GISTs. In addition, cell block for IHC staining requires adequate sampling, and because of this, endosonographers are frequently faced with ‘‘spindle cells’’ or ‘‘epithelioid cells’’ on smear rather than an IHC diagnosis. Thus, this descriptive diagnosis most likely reflects the performance of EUS-FNA in the general population. This low threshold of spindle or epithelioid cells on smear does, however, provide a ‘‘best case scenario,’’ likely overestimating sensitivity and decreasing specificity compared with an IHC diagnosis. Considering this, a sensitivity of 78.4% is still well below that of other published data. The most likely reason for this difference was the presence of an on-site cytopathologist to immediately review adequacy of samples in both studies quoting sensitivity O90%.12,16 In our study, a cytopathologist was present in only 18.9% (7/37) of EUS-FNAs. However, adequate tissue was obtained 100%
(7/7) of the time when a cytopathologist was available. Another reason for lower diagnostic yield and sensitivity in our study is that it likely more accurately reflects tissue yield as it is obtained in everyday practice. The fact that diagnostic yield did not differ significantly between the 2 different institutions in this study (77.8% MGH vs 80% BWH) supports this. In our study, the sensitivity of EUS-FNA cytologic examination for a GIST located in the stomach was 84.4% (27/ 32), whereas 0 of 3 tumors located in the duodenum yielded diagnostic cytologic findings. This underscores the importance of accessibility of the GIST because tumors located within the stomach are clearly more amenable to sampling than are those located in the small intestine. The sensitivity was also increased with increased tumor size, up to a threshold of 10 cm. The sensitivity was 80%, 87.5%, 100%, and 0% for tumors with size !2 cm, 2 to 5 cm, 5 to 10 cm, and O10 cm, respectively. These findings suggest that sensitivity correlated with tumor size for GISTs smaller than 10 cm. It was surprising that large tumors greater than 10 cm did not yield diagnostic cytologic material. One possible mechanism is that larger tumors are more prone to necrosis, which could potentially play a role in making FNA of these lesions more difficult. A review of the surgical histologic diagnoses of the 4 tumors greater than 10 cm revealed that 3 of 4 were noted to have areas of necrosis or patchy hemorrhage throughout. The fourth tumor had a large cystic component. Although it is unclear exactly how much these factors contributed, they may have had a role in determining the cytologic yield by interfering with adequate sampling. Of note, the study of Akahoshi et al al9 so found that tumor size correlated with diagnostic yield and sensitivity, although the authors did not find a threshold effect as described here. Our findings suggest that the sensitivity and diagnostic yield of EUS-FNA for the diagnosis of GIST compare favorably with other well-accepted indications of this procedure, such as sampling pancreatic lesions and lymph nodes. More conventional sampling techniques, such as forceps biopsy or EMR, are limited in their clinical utility, given the difficulty of sampling lesions in a subepithelial location and the increased risk for perforation, respectively. In addition, a clear role for EUS-guided Tru-cut biopsy has yet to be defined, given inconsistent results in its ability to provide adequate tissue yield. More studies will have to be done to further elucidate a well-defined role for these alternative sampling techniques. However, at present, EUS-FNA should be considered the procedure of choice to secure a tissue diagnosis of GIST. In examining features of GIST that are predictive of the ability to obtain adequate tissue yield, increasing size up to 10 cm, round/oval shape, and location in a specific sonographic wall layer were statistically significant in their ability to predict adequate tissue yield. Duodenal location, size O10 cm, irregular shape, and unclear sonographic wall
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Figure 2. A, EUS image of a GIST representative of the diagnostic cytology group (group A), showing a small round GIST located within a specific sonographic wall layer. B, EUS image of a GIST representative of the nondiagnostic cytology group (group B), showing a large irregular GIST located in an unclear sonographic wall layer (arrow).
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layer were significantly associated with inadequate tissue yield and thus with nondiagnostic cytology samples. Statistical significance was demonstrated for each anatomic factor studied, whereas none of the biologic or procedural factors were of significance. These findings demonstrate that EUS-guided FNA sampling may not necessarily be dependent on the histologic composition of the tumor. There was a trend toward intermediate/high risk histologic findings in the nondiagnostic group. However, this was likely because size represents 1 of the 2 criteria used in stratifying the malignant risk for GIST (mitotic count being the other), as described by Fletcher et al.19 The current study was underpowered to adequately assess procedural factors, such as needle gauge, number of needle passes, and the presence of a cytologist. Although it may be intuitive that more passes or use of a larger-bore needle would provide more tissue, this study does not demonstrate a clear association. It should be noted that only 1 to 2 needle passes were made in the majority of patients (73.1% in group A vs 83.3% in group B). However, the number of passes was not significantly different between the 2 groups (P Z 1.0). As is standard practice, this decision was made at the discretion of the individual endosongrapher and was based on a real-time assessment of presumed tissue adequacy and the risk/benefit ratio of further passes in each case. Despite lacking statistical significance, it is clear that when a cytologist was present, adequate tissue was obtained 100% (7/7) of the time compared with 73% (22/30) when a cytologist was not present. This trend merits attention because the presence of a cytologist could represent the added measure necessary to bridge the gap between a diagnostic yield of 78.4% as in this study and one approaching 100%. Given the predictive features described above, a tailored approach to EUS-FNA could be envisioned where the endosonographer uses an on-site cytopathologist when encountering a GIST tumor characterized by anatomic features predictive of inadequate tissue yield. Although not yet prospectively studied, this approach would most likely increase the yield while limiting the unnecessary overuse of a valuable resource. This study has several important strengths. The patient cohort was well defined and histologically based and, to our knowledge, represents the largest such cohort to date used to assess the role of EUS-guided FNA cytologic findings for the diagnosis of GIST. Although we are unable to calculate specificity, positive predictive value, negative predictive value, or diagnostic accuracy, our approach allowed an accurate calculation of both sensitivity and diagnostic yield. The calculation of only sensitivity and diagnostic yield does provide a statistical weakness that should be interpreted with caution. Nonetheless, we feel that these results significantly build on the very sparse and limited data available in this field. An additional strength of this study is that it included patients from 2 different medical centers, helping to protect against institutional bias and further increasing its generalizability.
There are also several weaknesses. Only 37 patients of the initial 460 collected from the pathology database fulfilled inclusion criteria and had EUS-guided FNA before surgical removal of the GIST. The majority of the other 423 did not undergo EUS-guided FNA because they either proceeded directly to surgical resection from radiologic imaging or their tumors were discovered on postmortem examination. Thus, we are studying a very small, select subpopulation of patients. This selection bias should be recognized, but likely only had a minimal effect on our results because the purpose of our study was to examine this select subpopulation, a group of patients where diagnosis and further management could possibly be aided by EUS-guided FNA. In addition, although this study is very large compared with other GIST or EUS studies, the patient cohort is rather small. This limited our ability to provide statistical power to detect significant differences, especially considering the number of factors that were studied. This was most evident when procedural factors were assessed, in which variations in needle gauge and number of passes and the presence/absence of a cytologist were too few to detect statistical significance. This also limited our ability to perform multivariate analysis. Given that only univariate analysis was performed, conclusions should be interpreted with caution. Although we are not able to determine the independence of particular variables, our results suggest that anatomic factors play a more important role in adequate sampling than do biologic factors. Considering this, we feel that univariate analysis is able to provide us with some basic conclusions in an area that has a sparsity of available data in the current literature. In conclusion, the sensitivity of EUS-FNA for the diagnosis of GIST is 78.4%, and it is influenced by size, location, shape, and layer of origin.
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ACKNOWLEDGMENTS We thank Shiva Gautam, PhD, for his help in reviewing the statistics in this article.
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Received July 16, 2008. Accepted November 20, 2008. Current affiliations: Division of Gastroenterology, Department of Medicine, Beth Israel Deaconess Medical Center (P.S.S.), Department of Pathology (M.B.P.) and Gastrointestinal Unit, Department of Medicine (W.R.B.), Massachusetts General Hospital, Division of Gastroenterology, Department of Medicine, Brigham and Women’s Hospital (J.R.S.), Boston, Massachusetts, Texas Digestive Disease Consultants, Baylor University Medical Center (B.M.), Dallas, Texas, USA. Presented at Digestive Diseases Week, May 21, 2007, Washington, DC (Gastrointest Endosc 2007;65:AB205). Reprint requests: William R. Brugge, MD, Gastrointestinal Unit, Massachusetts General Hospital, 55 Fruit St, Boston, MA 02114. If you want to chat with an author of this article, you may contact him at [email protected].