Morphologic features of GISTs. A) Spindle cell tumor infiltrating the submucosa and lamina propria of the colon. B) Epithelioid cell type tumor. C) Malignant GIST with prominent pleomorphism and high mitotic activity. D) Nuclear palisade feature of GISTs. E) Numerous scattered and patchy tumor infiltrating lymphocytes. F) Strong immunoexpression of CD 117.