Answer 1: D. Gastrointestinal stromal tumor.
Answer 2: D. All of the above.
Comment: Gastrointestinal stromal tumors (GIST) are of mesenchymal origin but are not common (2% of all gastrointestinal tumors). The definition for these tumors proposed in 2001 includes: "generally CD117+ and KIT or PDGFRA (platelet-derived growth factor receptor) mutation-driven GI tumors with histologic features of spindle cells, epithelioid and rarely pleomorphic morphology" (National Institute of Health GIST workshop, April, 2001). About 90% to 95% of GIST tumors are CD117-positive but in negative cases both identification of mutations in PDGFRA or DOG1 (discovered on GIST-1) can be used to make the diagnosis. Note that this association between a biomarker (c-Kit) and a specific cancer (GIST) is a statistical correlation using inferential logic. The association is not rigorous causal relationship. For experimental proof using the modern molecular version of Koch's postulates, comparative genomic pathobiology is now used. Click here for the comparative pathology.
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1. Laurini JA, Carter JE. Gastrointestinal stromal tumors: A review of the literature. Archives of Pathology and Laboratory Medicine. 2010; 134:134–141.