Chemotherapy Combined With or Without Short-Course Radiotherapy Versus Chemotherapy Alone as Neoadjuvant Therapy for High-Risk Locally Advanced Colon Cancer With pMMR/MSS

Locally advanced colon cancer, particularly T4 disease or colon cancer with bulky nodes, carries a poor prognosis and limited efficacy with neoadjuvant chemotherapy. In our previous small-sample phase II study, PD-1 inhibitor plus CAPOX chemotherapy combined with short-course radiotherapy yielded a marked improvement in the pCR rate compared with neoadjuvant CAPOX alone, though survival outcomes remain under follow-up. This prospective, multicentre, randomised, three-arm phase III study enrolls 480 patients with pMMR/MSS locally advanced high-risk colon cancer. Participants are randomised in a 2:2:1 ratio to three arms: short-course radiotherapy combined with chemotherapy and PD-1 inhibitor (25 Gy in 5 fractions of radiotherapy, followed by 4 cycles of CAPOX plus the PD-1 inhibitor serplulimab); chemotherapy plus PD-1 inhibitor (4 cycles of CAPOX combined with serplulimab); and chemotherapy alone (4 cycles of CAPOX). The primary endpoint is the 3-year event-free survival (EFS) rate. Secondary endpoints include the pCR rate, 5-year overall survival rate (5y OS), R0 resection rate, toxicity, surgical complications and quality of life.