[Three-year survival outcomes of neoadjuvant immunotherapy for local advanced rectal cancer with pMMR: a single-center report of 140 patients from Peking University Cancer Hospital].

Objective: To evaluate the long-term survival outcomes of neoadjuvant immunotherapy combined with chemoradiotherapy or chemotherapy in patients with mismatch repair-proficient (pMMR) local advanced rectal cancer. Methods: A retrospective case-series study was conducted. Clinical,pathological,and follow-up data were collected from 140 patients with pMMR local advanced rectal cancer who received neoadjuvant immunotherapy at the Gastrointestinal Cancer Center,Unit Ⅲ,Peking University Cancer Hospital,from June 2019 to September 2024. The study included 96 males and 44 females, with an age (M (IQR)) of 61 (13) years (range: 29 to 81 years). Among them,120 patients received neoadjuvant immunotherapy combined with chemoradiotherapy, and 20 received immunotherapy combined with chemotherapy. Follow-up was conducted through outpatient reviews and telephone interviews. The prognostic factors of overall survival (OS) and disease-free survival (DFS) were screened by univariate and multivariate Cox regression analysis. The Kaplan-Meier method was used to plot survival curves, and the Log-rank test was employed to compare survival differences between groups. Results: For the 140 patients with pMMR local advanced rectal cancer, the median OS and DFS time were not reached. The 1-and 3-year OS rates were 98.4% and 92.8%,respectively; the 1- and 3-year DFS rates were 89.7% and 73.2%,respectively. Postoperative pathological examination revealed that 35 patients (29.9%) achieved a pathological complete response,and 57 patients (48.7%) showed tumor regression grade 0 to 1. Univariate and multivariate Cox regression analyses indicated that postoperative lymphovascular invasion was an independent poor prognostic factor for OS in pMMR rectal cancer patients undergoing surgery after immunotherapy (HR=5.58,95%CI:1.36 to 23.0,P=0.017). The 3-year OS and DFS rates for patients achieving complete response (CR) after neoadjuvant therapy were 100% and 95.3%, compared to 88.5% and 60.1% for non-CR patients. The DFS of the CR group was significantly superior to that of the non-CR group (P=0.002). Conclusion: Neoadjuvant immunotherapy combined with chemoradiotherapy or chemotherapy demonstrates a favorable safety profile and high 3-year survival rates in patients with pMMR local advanced rectal cancer.