[A Case of Locally Advanced Ascending Colon Cancer in Which a Residual Tumor Was Detected Only in the Subserosal Layer after Neoadjuvant Chemotherapy].

A 68-year-old man diagnosed with ascending colon cancer(cT3[SS], cN2a, cM0)declined surgical treatment; therefore, systemic chemotherapy was administered. After 18 courses of systemic chemotherapy(mFOLFOX or FOLFIRI), the patient underwent laparoscopic right hemicolectomy. Preoperative colonoscopy and computed tomography did not detect any tumor, however histopathological examination revealed a viable residual tumor in the subserosal layer. The patient did not receive adjuvant chemotherapy and is alive with no recurrence 3.5 years after surgery. There is no consensus on the efficacy of neoadjuvant chemotherapy for colon cancer. In the case presented herein, neoadjuvant chemotherapy resulted in a clinically complete response, with a residual tumor only in the subserosal layer. Based on this case, for advanced colon cancer treated via neoadjuvant chemotherapy, curative resection may still be recommended over a watch-and-wait approach even if clinically complete response is achieved.