A Case Report of Clear Cell Sarcoma-like Tumor arising in the rectum

Clear cell sarcoma-like tumor of the gastrointestinal tract (CCSLGT) is an extremely rare mesenchymal tumor that occurs in the digestive tract, with the most common sites being the small intestine, followed by the stomach and colon. This case involves a clear cell sarcoma-like tumor occurring in the rectum. The patient is an 85-year-old female admitted to the hospital due to "recurrent protrusion of a mass at the anal orifice after defecation for more than two months." Abdominal CT suggested a nodular enhancement at the lower end of the rectum. Grossly, it appeared as a polypoid nodule, with a maximum diameter of 2 cm. Microscopically, the tumor cells were arranged in solid sheets and irregular nest-like clusters, with some arranged in a herringbone pattern; the tumor cells were epithelioid, oval or short spindle-shaped, and nucleoli were visible. Immunophenotypically, SOX10 and S100 proteins were diffusely and strongly positive, melanoma-related markers were not expressed, and gastrointestinal stromal tumor markers and myogenic markers were not expressed. FISH testing revealed EWSR1 gene rearrangement and no BRAF mutation, thus diagnosing the tumor as a clear cell sarcoma-like tumor of the gastrointestinal tract.