Metastatic Perivascular Epithelioid Cell Tumor of the Stomach: An Unusual Diagnosis

Abstract

Purpose: Perivascular epithelioid cell tumor (PEComa) is a very rare mesenchymal neoplasia composed of distinctive perivascular epithelioid cells with variable immunoreactivity for melanocytic and muscle markers. We report a case of metastatic gastric PEComa discovered incidentally in a 74-year-old previously healthy female who underwent an emergent esophagogastroduodenoscopy (EGD) for food impaction. She was noted to have a Schatzki's ring and a 5 mm sessile polyp in the body of the stomach. Polyp biopsies showed a submucosal neoplasm composed of variable polygonal cells with granular eosinophilic cytoplasm. Immunostains showed multifocal positivity for Smooth Muscle Actin and Microphthalmia Transcription Factor. More diffuse positivity noted for desmin and cathepsin-K, while S-100 protein, MART-1, HMB45, c-kit, DOG-1, pan-keratin and CAM5.2 were negative. The tissue morphology and accompanying immunophenotype was most consistent with malignant PEComa. A contrast-CT scan of the abdomen/pelvis showed diffuse liver metastases. PET scan revealed multiple liver lesions, retroperitoneal and abdominal lymphadenopathy, and C5 and S1 bony lesions consistent with metastatic disease. Patient is currently exploring therapeutic options along the lines of metastatic soft tissue sarcoma. Since relatively few cases of malignant PEComa have been reported, firm criteria for malignancy have yet to be established. A recently suggested criteria for malignancy includes: size >5.0 cm, mitotic count >1 per 50 high-power fields and necrosis. Differential diagnosis of PEComa includes gastrointestinal stromal tumors, melanoma, clear cell sarcoma, leiomyosarcoma. PEComas appear to arise most commonly at visceral (especially gastrointestinal and uterine), retroperitoneal, and abdominopelvic sites, with a subset occurring in somatic soft tissue and skin. Malignant PEComa can be very aggressive, leading to multiple metastases and death as expected with a high-grade sarcoma. Surgery seems to be the only approach for aggressive disease, as chemo and radiotherapy has not shown significant results. PEComas show a marked female predominance. At present this neoplasm does not have a known normal cellular counterpart and the natural history is often unpredictable. Our case highlights the fact that despite the small size, the gastric PEComas can behave in an aggressive manner and require careful followup and additional diagnostic evaluation to rule out metastatic disease. Further studies on additional cases with longer clinical follow-up are necessary to accurately predict the biologic behavior of these distinctive tumors.