Toripalimab Combined With Neoadjuvant Chemoradiotherapy as First-line Treatment for Locally Advanced，High-Risk，MSS Rectal Cancer

This study tests whether adding toripalimab — an immunotherapy drug — to standard chemotherapy and radiation therapy (chemoradiation) before surgery improves outcomes for people with locally advanced rectal cancer that is classified as MSS (a type that typically does not respond well to immunotherapy alone). **You may be eligible if...** - You are 18–75 years old - You have confirmed MSS or pMMR rectal cancer (adenocarcinoma type) - Your cancer is clinical stage T3-T4 with at least one high-risk feature (positive surgical margins, lymphovascular invasion, or involved lateral lymph nodes) - You have not received any prior cancer treatment for this diagnosis - Your blood counts and organ function are within acceptable ranges **You may NOT be eligible if...** - Your rectal cancer is squamous cell type - You have another active cancer - You are allergic to any component of the chemotherapy or immunotherapy - You have an active autoimmune disease (lupus, rheumatoid arthritis, IBD, etc.) - You have HIV, active hepatitis B or C Talk to your doctor to see if this trial is right for you.