[A Case of Stage Ⅳc dMMR Transverse Colon Cancer with Complete Response to Combination Therapy with Immune Checkpoint Inhibitor in Stage ⅣB Lung Adenocarcinoma].

The patient is a 72-year-old man. He was diagnosed as a duplication of left upper lobe lung adenocarcinoma cStage ⅣB and transverse colon cancer cStage Ⅳc. Because he had symptoms of atelectasis and esophageal stricture due to the progression of lung cancer, we decided to precede immunochemotherapy(CBDCA plus PEM plus pembrolizumab)for lung cancer. After the start of treatment, both lung and colorectal cancer were shrinking, but after the 3 courses of treatment, he developed intestinal obstruction due to transverse colon cancer. Because generalized peritonitis due to perforation of the colon by endoscopic stenting for the obstruction and then emergency surgery was performed. The resected transverse colon lesion was diagnosed as pathologically complete response. Lung cancer was also diagnosed as clinically complete response. Since his ADL decreased postoperatively, he is under observation without reintroduction of immunochemotherapy. Fourteen months have passed since the last administration, and no progression has been observed in either lung nor colon cancers. Pembrolizumab is considered to be successful in the patient with dMMR colorectal cancer lacking MLH1 and PMS2.