74-year-old woman was diagnosed with locally advanced unresectable transverse colon cancer. She started CAPOX therapy as first-line therapy after ileostomy. After second course, MSI-high was detected, so nivolumab plus ipilimumab combination therapy was started as second-line therapy. After 4 courses of combination therapy, she was judged to be in partial response and surgery was performed. Histopathological diagnosis of the surgical specimen showed complete response, and she is still alive without recurrence 15 months after surgery.