A KIT-negative, DOG1-positive epithelioid GIST of the stomach harboring a novel PDGFRA exon 14 single nucleotide deletion.

Gastrointestinal stromal tumors (GISTs) are the most common primary mesenchymal tumors of the gastrointestinal tract, and most of them harbor KIT or platelet-derived growth factor receptor alpha (PDGFRA) gain-of-function mutations. Proper diagnostic assessment of GISTs has become very important since the availability of the molecular-targeted therapy with imatinib mesylate. Histopathology remains the gold standard in GIST diagnosis, and immunohistochemistry plays the major confirmatory role. Moreover, genetic sequencing not only further confirms the diagnosis of GIST, but also provides information for the optimal treatment of patients. Herein, we describe a gastric GIST harboring a novel PDGFRA exon 14 frameshift mutation caused by a single-nucleotide deletion. The case reported here represents further evidence regarding the existence of a distinct subset of GISTs characterized by the PDGFRA mutation, the gastric localisation, the epithelioid morphology, and the weak or negative immunohistochemical expression of KIT. DOG1 is emerging as a promising biomarker for this subgroup of GISTs.