[A Case of Cecal‒Ascending Colon Cancer Achieved Complete Remission by Surgical Resection and Immune Checkpoint Inhibitor].

We have experienced a case in which MSI‒high advanced cecum and ascending colon cancer was completely cured by surgery and immune checkpoint inhibitors (ICIs). CEA, which had been high before surgery, did not normalize after radical surgery and rose again 1 year later. Although no obvious relapse findings could be identified by imaging tests such as CT and PET and examination laparoscopy, an increase in CEA was observed, so it was judged that the residual tumor had a flare‒up, and pembrolizumab alone was started. After 3 cycles, CEA normalized and treatment was completed after a total of 9 doses. Currently, no recurrence has been observed and follow‒up is underway. If there is a high suspicion of a recurrence of MSI‒high colorectal cancer, ICI therapy was considered an option.