[A Case of Gastrointestinal Stromal Tumor(GIST)of the Sigmoid Colon with Early Colon Cancer].

A 67-year-old male patient was referred to our department for fecal occult blood in March 2019. In April, lower intestinal endoscopic examination revealed a 25-mm pedunculated polyp in the sigmoid colon. Endoscopic mucosal resection was then performed. The pathological diagnosis was tub1-tub2 with an invasion depth of pT1b 3,000 μm, and ly0 and v1 vascular invasion. The tumor marker levels were normal, with CEA of 1.1 ng/mL and CA19-9 of 13.9 U/mL. An additional laparoscopic low anterior resection and D2 dissection were performed in June. After the endoscopic mucosal resection, pathologic examination revealed densely hyperplastic spindle cells arranged in bundles at the proper muscular layer of the scar site. There was no lymph node metastasis. On immunostaining, the lesion tested positive for c-kit, CD34, and DOG1, but negative for desmin, SMA, and S-100, with a MIB-1 index of 2%. The patient was diagnosed with very low risk gastrointestinal stromal tumor(GIST). We encountered a rare case of early sigmoid colon cancer, complicated by sigmoid colon GIST.