A 53 year old man presents with increasing gastric pain and is found to have a 3 cm mass located in the anterior wall of his stomach. This mass is resected and histologic examination reveals a tumor composed of cells having elongated, spindle-shaped nuclei. The tumor does not connect to the overlying gastric epithelium and is instead found only in the wall of the stomach. The tumor cells stain positively with CD117, but negatively with both desmin and S-100. Special studies find that these tumor cells have abnormalities of the KIT gene. Which of the following is the most likely diagnosis? a. Lymphoma of mucosa-associated lymphoid tissue (MALToma)
b. Ectopic islet cell adenoma (VIPoma)
c. Gastrointestinal stromal tumor (GIST)
d. Submucosal leiomyoma ("fibroid tumor")
e. Nonchromaffin paraganglioma (chemodectoma)