[Short-term efficacy and safety of neoadjuvant immunotherapy for locally advanced colon cancer with deficient mismatch repair].

Objective

To investigate the short-term efficacy and safety of neoadjuvant immunotherapy in patients with locally advanced colon cancer with deficient mismatch repair (dMMR) or microsatellite instability-high (MSI-H).

Methods

A retrospective analysis was conducted on the clinicopathological data of 21 patients with dMMR/MSI-H locally advanced colon cancer who received neoadjuvant immunotherapy followed by radical resection at the Cancer Hospital, Chinese Academy of Medical Sciences between February 2023 and December 2025. The short-term efficacy and safety of neoadjuvant immunotherapy and subsequent radical surgery were evaluated.

Results

Among the 21 patients, there were 15 male and 6 female, with a median age of 54 years (range, 33 to 79 years). Ten patients had ascending colon cancer, six had sigmoid colon cancer, four had transverse colon cancer, and one had descending colon cancer. No grade 4 or higher immune-related adverse events (irAEs) occurred in any patient after neoadjuvant immunotherapy. Grade 1 to 2 irAEs were occurred in 8 patients (38.1%, 8/21), and only 1 patient (4.8%, 1/21) developed grade 3 irAE. All patients underwent radical surgery after neoadjuvant immunotherapy, with R0 resection rate of 100.0% (21/21). No patient developed grade Ⅲ or higher postoperative complications. Only four patients (19.0%, 4/21) develpoed grade Ⅰ to Ⅱ postoperative complications, including anastomotic leakage in one patient (4.8%, 1/21), paralytic intestinal obstruction in 1 patient (4.8%, 1/21), intra-abdominal infection in 1 patient (4.8%, 1/21), and fever in 1 patient (4.8%, 1/21). Postoperative pathological results showed that all patients achieved tumor downstaging compared with the clinical stage before neoadjuvant therapy. Sixteen patients (76.2%, 16/21) achieved pathological complete response (pCR), and 18 patients (85.7%, 18/21) achieved major pathological response (MPR). With a median follow-up of 12 months (range, 3 to 37 months), no patient developed local recurrence or distant metastasis.

Conclusion

For patients with dMMR/MSI-H locally advanced colon cancer, preoperative neoadjuvant immunotherapy can achieve remarkable efficacy without increasing the risk of postoperative complications, representing a safe and effective therapeutic strategy.