[A Case of Colon Cancer with Peritoneal Dissemination and Liver Metastasis That Responded to Comprehensive Treatment by Perioperative Chemotherapy and Cytoreductive Surgery].

A 64-year-old man was referred to our hospital to determine the cause of fecal occult blood. Colonoscopy revealed a type Ⅱtumor located in the ascending colon. Histopathologic analysis of the tumor biopsy specimen revealed moderately differen- tiated, tubular adenocarcinoma with KRAS exon 2(G12V)mutation. FDG-PET/CT revealed high trace accumulation in the S4 of the liver and in multiple sites spread across the abdominal cavity(cT4aN1M1c2[H1, P3], cStage Ⅳc). Chemotherapy using S-1 plus oxaliplatin(SOX)with bevacizumab(Bmab)was administered. After 8 courses of SOX with Bmab, the volume of the ascending colon cancer and liver metastasis reduced, and peritoneal disseminations disappeared. We, therefore, considered that curability B resection was suitable, and performed right hemicolectomy, total omentectomy, and resection of the rectovesical peritoneum. Histopathological examination of surgical specimens revealed extensive fibrosis from the submucosa to subserosal tissue with some tubular adenocarcinoma cells(histological effect: Grade 2). For maintenance therapy, trifluri- dine/tipiracil plus Bmab was administered after cytoreduction. The patient is in remission for 26 months without recurrence. Perioperative chemotherapy and cytoreductive surgery are useful for the treatment of colon cancer with diffuse peritoneal dissemination.