Node-Sparing Low-Dose Radiotherapy Concurrent With Chemotherapy and PD-1 Inhibitor in pMMR/MSS High-Risk Locally Advanced Colon Cancer: A Prospective, Single-Arm, Phase II Trial

Most colorectal cancers belong to the microsatellite stable (MSS) or proficient mismatch repair (pMMR) subtypes, with limited response to PD-1 inhibitors. Radiotherapy can increase the release of tumor-associated antigens, thereby improve responsiveness to PD-1 blockade in MSS/pMMR rectal cancer. Tumor-draining lymph nodes are important sites for PD-1 inhibitors to exert antitumor effects, and studies have reported that direct radiation-induced damage and fibrosis can inhibit lymph node drainage and anti-tumor function. Accumulating evidence indicates that low-dose radiotherapy reprograms the tumor microenvironment (TME), transforming immunosuppressive 'cold' tumors into immunostimulatory 'hot' tumors. This transition is mediated by modulating the gut microbiota, eliciting innate and adaptive immune responses, inhibiting immunosuppressive cells, and promoting the infiltration of T and B lymphocytes.Therefore, this study aims to evaluate whether node-sparing low-dose radiotherapy (1Gy/8f) concurrent with chemotherapy and PD-1 inhibitor can improve the pathological complete response (pCR) rate, enhance tolerability, and improve prognosis in patients with pMMR/MSS high-risk locally advanced colon cancer.

NCT Number	NCT07279077
Lead Sponsor	Sixth Affiliated Hospital, Sun Yat-sen University
Conditions	Colon Cancer, Neoadjuvant Therapies, Immune Checkpoint Therapy, Radiation Therapy
Enrollment	38 participants
Start Date	2025-11-26
Primary Completion	2030-11-25 (estimated)
Study Completion	2031-12-30 (estimated)
Updated on ClinicalTrials.gov	2025-12-26