Cytokeratin-positive gastrointestinal stromal tumor of biphasic morphology: a case report.

Gastrointestinal stromal tumor (GIST), which is associated with mutations in KIT or a platelet-derived growth factor receptor, alpha polypeptide (PDGFRA), is the most common mesenchymal tumor of the gastrointestinal tract[1]. A definitive diagnosis of GIST is important to ensure administration of effective drugs, such as imatinib mesylate, and immmunohistochemical staining for c-Kit or DOG1 is useful for the diagnosis. According to previous studies, cytokeratin (CK) expression is a rare event in GISTs[2-6], so they can easily be misdiagnosed as other epithelial or epithelioid mesenchymal tumors. In such cases, a diagnosis of GIST can be made when DOG1 immunoreactivity or mutation of KIT or PDGFRA are observed.