Gastric Spindle Cell Neoplasms With Mast Cells - A Pitfall In Diagnosis Of Gastric Biopsies.

Abstract

Abstract Introduction/Objective Undifferentiated sarcoma, previously known as malignant fibrous histiocytoma (MFH), is a very rare primary neoplasm of stomach. It usually arises from soft tissue of extremities with an incidence of 1- 2/100,000, typically presenting in the 5th-7th decades of life with a slight male predominance. We report a case of gastric undifferentiated sarcoma which was interpreted as gastrointestinal stromal tumor (GIST) on initial biopsy. Methods/Case Report A 84 year old female presented to the Danbury Hospital emergency department with hematemesis and melena. Upper gastrointestinal endoscopy revealed a pedunculated mass in the cardia of stomach with ulceration, followed by a computed tomographic scan of chest and abdomen revealing a 2.9 cm mass along the proximal lesser curvature of the stomach. An endoscopic biopsy revealed a spindle cell neoplasm with immunohistochemical staining for c-kit consistent with GIST. She later underwent partial gastrectomy. Histopathology of the resected gastric tumor showed tumor cells arranged in sheets and storiform pattern, exhibiting spindled to polygonal morphology with marked nuclear pleomorphism, high mitotic activity (20 mitoses per 10 high power fields) and Touton type giant cells. Immunohistochemical stains demonstrated absence of staining for c-kit, DOG-1, CD34, actin, desmin, S100, cytokeratin AE1/AE3, CD3, CD5, CD20, CD21, CD15, CD30, ALK1, myeloperoxidase, CD1a and LCA. Numerous mast cells within the tumor stained for c-kit. Molecular testing for c-kit and PDGFRA mutations were negative. A final diagnosis of undifferentiated sarcoma with features of myxofibrosarcoma was rendered. Results (if a Case Study enter NA) NA. Conclusion Undifferentiated sarcomas are high grade malignant mesenchymal neoplasms without clear cellular differentiation or immunohistochemical marker. Only 4% of the total cases of undifferentiated sarcoma have been reported to be arising primarily from the gastrointestinal tract. They carry a poor prognosis with a 5 year survival of 47%. The main pitfall in our case was the positive uptake of c-kit stain by mast cells which led to the diagnosis of GIST in first gastric biopsy. We want to stress the importance of entertaining this diagnosis in the differential when encountered with a malignant gastric spindle cell neoplasm along with careful interpretation of c-kit stains in small biopsy specimens as the treatment and prognosis differs greatly from GIST.