Neoadjuvant immunotherapy in a locally advanced colon cancer patient with MSI-H and suspected Lynch syndrome: A case report.

Carrilizumab, a PD-1 inhibitor, has shown therapeutic effectiveness in patients with late-stage or metastatic solid tumors exhibiting DNA mismatch repair deficiency (dMMR) or microsatellite instability-high (MSI-H). dMMR/MSI-H cancer patients are known to be responsive to PD-1 inhibitors. However, the use of carrilizumab for preoperative immunotherapy in early, unresectable MSI-H/dMMR primary colon cancer lesions is relatively underexplored. We present the case of a 46-year-old male who sought medical attention at our institution due to a history of hematochezia for two weeks, right-sided abdominal pain for one week, and loose stools. Imaging indicated duodenal involvement, and a biopsy confirmed ascending colon adenocarcinoma with MSI-H status. Given that the patient's family exhibited a history of more than three confirmed cases of colorectal cancer spanning two generations, Lynch syndrome was considered. After four cycles of PD-1 antagonist immunotherapy with carrilizumab, the patient's symptoms resolved, and physical examination revealed no abdominal tenderness or palpable masses. Following radical colectomy, the primary tumor exhibited a pathological complete response. This case highlights the potential of preoperative neoadjuvant immunotherapy to improve staging accuracy and increase surgical resection rates in T4b MSI-H colon cancer patients without distant metastasis, suggesting a need for reconsideration of the treatment approach.