Quiz. What is your diagnosis?

CT scan of the abdominal cavity of a 48-year-old woman revealed extensive thickening of the wall of the pyloric region of the stomach (Fig. 1). During surgery, a gastric tumor was found involving the distal part of the body and the pyloric region of the stomach. The stomach was resected and both macroscopic and histological examination of the surgical specimen showed diffuse neoplastic infiltration covering the full thickness of the stomach wall (Fig. 2) and passing to the surrounding adipose tissue. The tumor texture was built partly of spindle cells forming herring-bone fascicles (Fig. 3), partly of epithelioid cells (Fig. 4, insert) or small round & short spindle cells (Fig. 4). They created hemangiopericytoma-like arrangements (Fig. 5) or formed solid sheets separated by fibrous or myxoid stroma (Fig. 6). Immunohistochemically, tumor cells were characterized by the positive reaction to cytokeratins (AE1/AE3) (Fig. 7), EMA, vimentin (Fig. 8) and Bcl2 antigen (Fig. 9), but did not present reaction against smooth muscle actin, S100 protein, and CD20, HMB45, SOX10, CD31, CD34, CD99 and CD117.