Long-term survival and treatment efficacy in dMMR/MSI-H rectal cancer: A real-world cohort from seven large medical college–affiliated hospitals.

Abstract

3601 Background: Neoadjuvant immunotherapy provides considerable advantages for patients with dMMR/MSI-H rectal cancer. However, treatment strategies in real-world settings vary depending on tumor characteristics, economic conditions, and the choices made by physicians and patients. Methods: We screened more than 10,000 rectal cancer cases from seven large medical college-affiliated hospitals. We used the Kaplan-Meier curve to compare survival and progression, applied Cox regression to analyze impact factors, and examined tumor regression grades with chi-square analysis. Results: From March 2010 to April 2024, 502 patients were enrolled and diagnosed with dMMR/MSI-H rectal adenocarcinoma through immunohistochemistry or PCR. 100 patients underwent neoadjuvant immunotherapy, demonstrating a 96.34% 5-year overall survival (95% CI: 86.08-99.08%), and 90.74% 5-year disease-free survival (95% CI: 74.67-96.82%). This indicated a 16.50% enhancement in overall survival (p = 0.042) and a 16.87% increase in disease-free survival (p = 0.002) compared to conventional chemoradiotherapy (5-year OS: 79.84%, 95% CI: 71.69-85.87%; 5-year DFS: 73.87%, 95% CI: 65.15-80.73%). Neoadjuvant immunotherapy demonstrated significant superiority in tumor regression (p < 0.0001), however, the combination with chemotherapy did not enhance the effect (p = 0.622), and varying chemotherapeutic agents did not improve tumor regression in conventional chemoradiotherapy either. Additionally, elevated serum CEA levels were associated with an increased risk of both death and disease progression. Patients with advanced age, lower clinical stages, and fewer risk factors were more likely to undergo direct surgical resection. Conclusions: Neoadjuvant immunotherapy is advantageous for dMMR/MSI-H rectal cancer patients, as it leads to better tumor regression and enhanced disease control.