Gastrointestinal Kaposi Sarcoma Involving Stomach and Colon: Diagnostic Pitfall for Pathologists with Expression of CD117.

Kaposi sarcoma (KS) is a low-grade vascular tumor caused by human herpes virus type 8 (HHV8). Gastrointestinal involvement of KS is rare and most commonly clinically silent. Gastrointestinal KS may mimic gastrointestinal stromal tumors (GISTs) histologically as the tumor formed by morphologically spindle-shaped cells, which is mostly located in the mucosa and submucosa. In the present study, we describe a case of Kaposi sarcoma that was first diagnosed in the gastrointestinal tract of a 73-year-old female patient who presented to the clinic with nausea and diarrhea. Immunohistochemical staining showed cytoplasmic CD117 expression both in stomach and colon biopsies. Although involvement of KS is rarely seen in the gastrointestinal tract (GIT), the differential diagnosis of low-grade spindle cell lesions without significant pleomorphism, KS should definitely be considered, and it should be known that CD117 positivity is also present in these neoplasms.