Node-Sparing Short-Course Radiotherapy Plus Chemotherapy, Bevacizumab and PD-1 Inhibitor in Metastatic pMMR/MSS Colorectal Cancer (MODIFI-CRC)

The current standard first-line treatment for metastatic colorectal cancer is chemotherapy combined with targeted therapy, yet the prognosis remains poor. Although combining immunotherapy, anti-angiogenic agents, and chemotherapy has shown some efficacy in MSS/pMMR metastatic patients, progression-free survival (PFS) remains suboptimal. Radiotherapy-particularly high-dose radiotherapy-can enhance tumor antigen release and potentially improve the response of MSS/pMMR colorectal cancer to PD-1 inhibitors. Tumor-draining lymph nodes (TDLNs) are key sites for PD-1-mediated anti-tumor activity, but radiation-induced damage and fibrosis may impair their immune function. Prior studies have reported a remarkable pathologic complete response (pCR) rate of 77.8% using node-sparing radiotherapy in locally advanced rectal cancer. This phase II/III study aims to evaluate whether node-sparing modified short-course radiotherapy combined with chemotherapy, bevacizumab, and PD-1 blockade can improve objective response rate (ORR) in phase II and progression-free survival (PFS) in phase III, together with treatment tolerance, and overall prognosis in patients with pMMR/MSS metastatic colorectal cancer.