FIRM: A Pospective, Single-arm, Multicenter Clinical Trial Evaluating Preoperative Neoadjuvant mFOLFOX6 Chemotherapy in Combination With PD1 Monoclonal Antibody in MSS/pMMR Locally Advanced Rectal Cancer

Preoperative neoadjuvant chemoradiotherapy can induce tumor regression and reduce the risk of postoperative recurrence, serving as the standard treatment for locally advanced rectal cancer. However, neoadjuvant radiotherapy may increase the risk of postoperative complications, proctitis, enteritis, and reduced anal function. Exploring radiation-free approaches to prevent the effects of radiotherapy toxicity on postoperative complications and quality of life is now a significant research focus. Neoadjuvant chemotherapy represents a promising approach in the neoadjuvant treatment of rectal cancer. Neoadjuvant chemotherapy avoids the impact of radiotherapy on organ function, reduces the incidence of postoperative anastomotic leakage, and is beneficial for long-term anal function preservation. However, its low tumor regression rate limits its application in the neoadjuvant treatment of rectal cancer. For patients with locally advanced rectal cancer, there is an urgent need for a new neoadjuvant treatment strategy that can both significantly improve tumor regression rates and reduce the risk of postoperative anastomotic leakage, and protect long-term anal function. PD-1 inhibitors are highly effective in treating microsatellite instability-high (MSI-H) colorectal cancer patients, but show poor efficacy in the 95% of patients with microsatellite stable (MSS) tumors. The challenge now is to find combination therapies that can convert tumors into an "immune-activated tumor," thereby enhancing the effectiveness of immunotherapy in MSS patients. Oxaliplatin and 5-fluorouracil have roles in releasing tumor antigen epitopes, activating CD8+ cells, and reshaping the immune microenvironment. Multiple clinical studies and animal experiments have shown that combining PD-1 antibodies with FOLFOX generates a synergistic effect, showing strong antitumor activity. This study evaluates the efficacy, safety, and impact on postoperative anal function of preoperative neoadjuvant treatment with FOLFOX chemotherapy combined with PD-1 inhibitors in patients with MSS-type advanced rectal cancer. The radiotherapy-free approach aims to avoid radiotherapy-related toxicity, offering significant potential to enhance the efficacy of neoadjuvant chemotherapy, improve long-term survival, and protect anal function.