Gastrointestinal stromal tumors (GIST) are the most common mesenchymal neoplasms of the digestive tract. They are relatively rare neoplasms compared with gastrointestinal carcinomas and usually can readily be differentiated from carcinomas based on the morphology of the neoplastic cells that are typically spindled (70%), pure epithelioid, or mixed type. GISTs in general lack expression of cytokeratin and exhibit immunoreactivity toward CD117, CD34, or DOG1. GISTs can demonstrate a pure epithelioid morphology that can appear similar histologically to a carcinoma. Very few epithelioid GISTs have been reported to express cytokeratin, which can lead to diagnostic challenges especially in cases with pure epithelioid morphology. Epithelioid GISTs should be considered in the differential diagnosis when evaluating gastrointestinal neoplasms with overlapping epithelioid and carcinoma-like morphology. An accurate diagnosis can be made using additional immunohistochemical studies directed against CD117, CD34, or DOG1. Advanced investigations such as mutation analysis of KIT using molecular pathology methods can further assist in confirming the diagnosis.
*Department of Pathology & Laboratory Medicine, University of Saskatchewan, St Paul’s Hospital, Saskatoon, SK
†Department of Pathology, BC Cancer Agency, University of British Columbia, Vancouver, BC, Canada
The authors declare no conflict of interest.
Reprints: Nick Baniak, MD, Department of Pathology & Laboratory Medicine, University of Saskatchewan, St Paul’s Hospital, 103 Hospital Drive, Saskatoon, SK, Canada S7N 0W8 (e-mail: firstname.lastname@example.org).
Received November 22, 2016
Accepted December 4, 2016