Histologic subtypes of GISTs. a Spindle cell type. The tumor is composed of fusiform spindle cells with a fascicular growth pattern. b Epithelioid type. The tumor is composed of large round or polygonal cells with abundant, often eosinophilic or clear cytoplasm. c Mixed type. The tumor is composed of mixture of both types (hematoxylin and eosin staining, original magnification x400).