[654] PEComas of the Gastrointestinal Tract and Mesentery: Clinicopathologic Study of 25 Cases with Evaluation of Prognostic Parameters

JL Hornick, CDM Fletcher. Brigham & Women's Hospital, Boston

Background: PEComas (perivascular epithelioid cell tumors) are distinctive mesenchymal neoplasms that most often arise in retroperitoneum, visceral organs, and abdominopelvic sites and usually show reactivity for melanocytic and smooth muscle markers. Fewer than 20 PEComas of the gastrointestinal (GI) tract have been reported, and behavior and criteria for malignancy are incompletely defined. The purpose of this study was to examine the clinicopathologic features of GI PEComas and to evaluate prognostic parameters.
Design: 25 PEComas of the GI tract and mesentery were retrieved from consult and surgical files. Clinical and pathologic features were evaluated, and immunohistochemistry was performed. Clinical follow-up was obtained from medical records and referring physicians. Statistical analysis was performed using Fisher exact test.
Results: 13 patients were female and 12 male (median age 46 yr; range 7–70 yr). One patient had tuberous sclerosis. 14 tumors arose in the colon, 8 small bowel, and 1 each stomach, omentum, and duodenum. Median size was 7 cm (range 0.8–22 cm). Two tumors were limited to mucosa and submucosa, 3 extended to muscularis propria, 12 to subserosa, and 7 into mesentery; 2 tumors had lymph node metastases. Mucosal ulceration was present in 10 cases. The tumors were composed of nests and sheets of usually epithelioid cells with abundant granular eosinophilic to clear cytoplasm, surrounded by a delicate capillary vasculature. Nine tumors had mixed epithelioid and spindle cell components, and 1 was predominantly spindled. 13 tumors showed marked nuclear atypia. 12 tumors contained occasional pleomorphic cells, and 9 showed diffuse pleomorphism. Median mitotic rate was 5 per 10 HPF (range 0-36). Vascular invasion was present in 2 cases, and 13 had necrosis. By IHC, 16/25 were positive for HMB-45, 18/23 melan-A, 13/21 MiTF, 13/25 SMA, 18/25 desmin, and 4/24 focal cytoplasmic S-100. One case each was positive for KIT, EMA, keratin, and TFE3. Follow-up was available for 21 patients (median 3 yrs; range 2-111 months). Eight patients developed metastases (6 liver, 3 peritoneum, 2 lung, 1 bone). Thus far, 4 patients died of disease. Metastases were significantly associated with tumor size ≥7 cm (p=0.02), marked atypia (p<0.001), diffuse pleomorphism (p=0.01), and mitoses ≥5 per 10 HPF (p<0.001).
Conclusions: The colon is the most common site for GI PEComas, which range from benign lesions to aggressive, high grade sarcomas. The presence of marked nuclear atypia and mitotic activity are the strongest predictors of malignant behavior.
Category: Gastrointestinal

Tuesday, March 23, 2010 1:00 PM

Poster Session IV # 57, Tuesday Afternoon


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