A case of an enlarged rectal adenoma while achieving a clinical complete response with chemotherapy for advanced rectal cancer.

The effect of chemotherapeutic agents on concomitant colorectal adenomas in patients with advanced colorectal cancer is not clear. We report a case of an enlarged rectal adenoma while achieving a clinical complete response with chemotherapy for an advanced rectal adenocarcinoma. A 78-year-old man was referred to our hospital for evaluation of bloody stools. The clinical diagnosis was an advanced lower rectal adenocarcinoma with para-aortic lymph node metastases, and a sessile polyp on the proximal aspect of the rectal tumor. The rectal adenocarcinoma was treated with chemotherapy, including 1 cycle of capecitabin plus oxaliplatin (CapeOX), 22 cycles of tegafur/gimeracil/oteracil (S-1) plus irinotecan (IRIS), and 1 cycle of tegafur (UFT) plus calcium folinate (LV). One year after the last course of chemotherapy, colonoscopy showed a scar without visible rectal tumor; CT imaging confirmed no para-aortic lymphadenopathy. The patient had a clinical complete response to chemotherapy. In contrast, the polyp increased in size. The polyp was removed by endoscopic mucosal resection (EMR). The pathologic evaluation showed a well-differentiated tubular adenocarcinoma with adenoma localized in the mucosa. No recurrence of the advanced adenocarcinoma or intramucosal adenocarcinoma with adenoma occurred for 2 years after EMR. This case indicates the importance of careful surveillance for synchronous adenomas, even in patients with advanced colorectal cancer.