Fig. 2.

(A) Cut-section reveals the well-defined tumor measuring 3.9 × 2.7 cm covered by intact mucosa. The tumor is located in the proper muscle with extension to the subserosa and shows a homogeneous yellow to white, firm surface. (B) The tumor is well-circumscribed, but not encapsulated, and located in the proper muscle (H&E, ×20). (C) The tumor shows characteristic hypocellular sclerosis, with wavy collagen and scattered mononuclear inflammatory infiltrates (H&E, ×100). Note the sparse spindle cells dispersed among thick collagen bundles and some plasma cells (inset, H&E, ×400). (D) Occasional psammomatous and dystrophic calcifications are found (H&E, ×100). (E) Spindle cells show no immunoreactivity for CD117 (CD117, ×100). Note the immunoreactive mast cells, as the internal positive control (inset, CD117, ×400). (F) Spindle cells show no immunoreactivity for smooth muscle actin (SMA, ×200). Note the immunoreactive vascular walls, as the internal positive control.