A Case of Advanced Colon Cancer that Achieved Pathological Complete Response after Administration of Pembrolizumab

Abstract

A 60-year-old woman started systemic chemotherapy with capecitabine/oxaliplatin and bevacizumab for advanced transverse colon cancer with abdominal wall invasion, advanced lymph node metastasis, and peritoneal dissemination. Since pathological examination of the biopsy specimen confirmed microsatellite instability-high (MSI-H) status at the end of the first course, the therapy was changed to pembrolizumab. After administration of pembrolizumab, penetration due to tumor shrinkage worsened, so infection control, such as ileostomy, was required. After 4 courses of pembrolizumab, computed tomography showed that the primary tumor had shrunk significantly, and ascites had disappeared. Laparoscopic extended right hemicolectomy and D3 lymph node dissection were then performed. Histopathological examination of the resected specimen showed no residual tumor cells, indicating pathological complete response. A case that supports the specificity of pembrolizumab for MSI-H colorectal cancer is reported.