[A Case of Pembrolizumab Therapy Markedly Effective for Advanced Recurrent Colorectal Cancer].

We report a case of pembrolizumab therapy as the fourth-line therapy for colorectal cancer and multiple lymph node recurrence with high-frequency microsatellite instability(MSI-High). The patient was a 75-year-old woman diagnosed with ascending colon cancer(pT4aN2bM0, Stage Ⅲc)and underwent laparoscopic right hemicolectomy, D3 dissection, and functional end-to-end anastomosis after inserting a self-expandable metallic stent. Postoperative adjuvant chemotherapy was performed, and the patient was followed. Postoperative 1 year 8 months, lymph node recurrence was indicated, and FOLFOX plus panitumumab therapy was introduced. FOLFIRI plus ramucirumab therapy and FTD/TPI were introduced as the second-line and third-line treatments, respectively; however, recurrent lymph nodes were further exacerbated and showed treatment resistance. Lymph node biopsy confirmed MSI-High, and pembrolizumab therapy was initiated as the fourth-line treatment. After the therapy, the lymph nodes reduced markedly. The patient remains undergoing chemotherapy without any adverse events.