[Two Case Reports of Complete Response to Pembrolizumab in MSI-H Colorectal Cancer].

Case 1:A 75-year-old woman with a history of Lynch syndrome developed a new ileocolic anastomotic tumor after prior surgeries for colorectal and ovarian cancers. Pembrolizumab led to clinical complete response after 5 courses, confirmed by endoscopy and PET-CT. Treatment was stopped after 15 courses at the patient's request, with no recurrence at 4 months. Case 2:A 69-year-old man underwent resection for descending colon stenosis, diagnosed as endocrine cell carcinoma (pStage Ⅲc, MSI-H). Postoperative PET-CT revealed lymph node metastasis. Pembrolizumab achieved clinical complete response after 10 courses;therapy was stopped after 18 courses, with response maintained at 9 months.