[A Case of Pathological Complete Response Post‒Pembrolizumab Therapy for Recurrent Liver Metastasis of Ascending Colon Cancer].

A female patient in her 70s, underwent laparoscopic right hemicolectomy for ascending colon cancer (pT4aN2aM0). Eight courses of post‒operative adjuvant chemotherapy with CapeOX were administered. However, 1 year and 5 months post‒surgery, liver metastasis was observed. Following 1 course of FOLFIRI therapy and 1 course of FOLFIRI+bevacizumab therapy, high‒frequency microsatellite instability (MSI‒H) was detected, and pembrolizumab therapy was initiated. CT imaging revealed necrotic changes in the metastatic lesion while stable disease (SD) was maintained. After completing 28 courses of pembrolizumab therapy over 1 year and 9 months, the treatment was temporarily discontinued. One year and 3 months after discontinuation, the CEA level was elevated and the tumor was enlarged. Pembrolizumab therapy was resumed, and 5 additional courses were administered. Subsequently, surgical resection of the liver metastasis revealed no residual tumor and pathological complete response was confirmed. The patient has remained recurrence‒free without further treatment.