Immunohistochemistry of the atypical tumor cells revealed positive immunoreactivity for smooth muscle actin (SMA) and vimentin, and focal immunoreactivity for cluster of differentiation (CD)34, Ki-67, leukocyte common antigen (CD45), desmin and S-100; however, staining for cytokeratin, CD117 and discovered on GIST (DOG)-1 protein was negative. The gene discussed is KIT; the disease is gastrointestinal stromal tumor.