Round cell epithelioid GIST (gastrointestinal stromal tumour) in an endoscopic biopsy is a diagnostic confounder.

1 of 2 DESCRIPTION The authors present a case of a 53-year-old lady, with vague upper gastrointestinal symptoms and progressive iron defi ciency anaemia, stool positive for occult blood and progressive weight loss. Endoscopically a lumenally protruding mass, with extensive mucosal ulceration was seen. Carcinoma, stromal tumour and lymphoma were the clinical differential diagnoses. Histologic sections showed a dense, diffuse and adhesive mucosal infi ltrate of round cells. The tumour cells were round, with high nuclear – cytoplasmic ratios, without any specifi c cyto-architectural attribute except rare subtle plasmacytoid aspect ( fi gures 1 and 2A,B ). A non-Hodgkin lymphoma and poorly differentiated adenocarcinoma were initially considered, and immunochemistry requisitioned. The initial sets of immunomarkers showed the infi ltrating cells to be negative for epithelial markers – pan-cytokeratin (CK), antiepithelial membrane antigen and CK 7, or leucocyte, B lymphocyte and plasma cell lineage markers (antileucocyte common antigen, CD 20,CD 79a, CD 138 and CD38). The second phalanx of immunostains included antihuman melanoma antigen (HMB) 45, Vimentin, S-100, Desmin, Ki-67, CD 117 and CD 34. The tumour cells were observed to diffusely label with CD117, vimentin and CD34, and unmarked by HMB 45, S-100 (melanoma markers) and desmin (muscle). With this immunoprofi le, a histologic diagnosis of gastrointestinal stromal tumour (GIST) was rendered and was confi rmed upon examination of the surgical resection specimen ( fi gure 2C ). Gastrointestinal stromal tumours are the most common mesenchymal tumours affecting all segments of the gastrointestinal tract, arising from the interstitial cells of Cajal, in the muscularis propria. These tumours equally affect female and male patients, with more than 75% of the cases occurring in patients older than 50 years. Five per cent of the lesions arise in the oesophagus, 50% in the stomach, 25% in the small bowel and 10% in the colon and rectum. 1 – 3 GISTs in 70% of cases are composed of spindle cells, in 20% of epithelioid cells, and the remainder have a mixed cellular composition. 3 GISTs with epitheloid features often have large polygonal cells with abundant Images in...