[A Case of MSI-H Sigmoid Colon Cancer with Para-Aortic Lymph Node Metastasis Treated with Pembrolizumab and Radical Resection].

A 60-year-old male was admitted to the hospital with abdominal pain and diagnosed with microsatellite instability-high (MSI-H)sigmoid colon cancer. Computed tomography revealed an obstructive mass in the sigmoid colon along with swelling of the para-aortic lymph nodes. The patient initially underwent loop transverse colostomy, followed by treatment with the immune checkpoint inhibitor(ICI)pembrolizumab. After 5 courses of ICI, the tumor significantly shrank; therefore, radical resection was performed. The patient has been monitored without adjuvant chemotherapy, and recurrence has not occurred after 1 year. This case shows that ICI may be an effective rescue treatment for colorectal cancer patients with unresectable distant metastasis.