DOG1, “discovered on GIST 1” encodes for a protein of unknown function that is highly sensitive and specific for gastrointestinal stromal tumors (GIST). GISTs occur in bowel walls and proposed to originate from the interstitial cells of Cajal. The majority of GISTs harbor activating mutations in KIT but approximate 5-15% of GIST are negative for c-Kit by immunohistochemistry, mainly associated with mutations in the PDGFRA gene. Antibodies against DOG1 have shown to be highly sensitive and specific, demonstrating 98-100% reactivity to GIST. DOG1 staining pattern is cytoplasmic and membranous, staining tumor cells and interstitial cells of Cajal. Its sensitivity was deemed superior to c-Kit; many cases with PDGFRA mutations were DOG-1 positive, but failed to show c-Kit reactivity.