Neoadjuvant PD-1 blockade in mismatch repair-deficient or microsatellite instability-high, locally advanced and resectable colorectal cancer: A retrospective real-world analysis.

185 Background: Neoadjuvant PD-1 blockade therapy has shown encouraging efficacy in patients with mismatch repair- deficient (dMMR)/microsatellite instability-high (MSI-H) locally advanced colorectal cancer. However, data from the real-world setting are scarce. Methods: We retrospectively collected clinical data of patients with dMMR/MSI-H locally advanced colorectal cancer diagnosed between 2022-2024 that received neoadjuvant anti-PD-1 monotherapy at the First Affiliated Hospital of Zhengzhou University. Pathological complete response, clinical complete response, R0 resection rate, and safety were analyzed. All statistical analyses were conducted using SPSS Statistics, version 22.0. Results: A total of 45 patients were enrolled. As of the data cutoff (Sep 15, 2024), the median follow-up was 14.0 months (range: 4.0-31.4). The median age was 53 years (range: 29.0–78.0) and 25 (55.6%) of 45 patients were male. 32 (71.1%) patients had clinical stage III disease and 39 (86.7%) patients had colon cancer. A higher proportion of patients (53.3%) had clinical T4 stage. 37 patients underwent the surgery of whom 29(78.9%) had a pathological complete response. The R0 resection was 100%. The median treatment duration was 4 cycles (range: 2-10). Among the 18 patients who received equal to or less than 4 cycles, the pCR rate was 77.8%, while for the remaining 17 patients who had more than 4 cycles of treatment, the pCR rate was 84.2%. Eight other patients had a clinical complete response and chose the watch and wait strategy. Treatment-related adverse events ≥3-4grade were observed in 3 patients. All patients survived without any disease recurrence. Conclusions: In this retrospective analysis, anti-PD-1 monotherapy is effective and tolerable for patients with dMMR/MSI-H locally advanced colorectal cancer. This study shows that pCR rate increases is associated with a longer treatment cycles probably. Further analysis of larger real-world datasets with longer follow-up will be essential to validate these results.