The Efficacy and Safety of Short-course Radiation Combined With Adebrelimab and CAPEOX Neo-adjuvant Therapy for Organ-retention in Patients With MSS/pMMR Ultra Low Rectal Adenocarcinoma

This study is testing a combination approach before surgery for patients with rectal cancer located very close to the anus — using a short course of radiation plus immunotherapy (adebrelimab) and chemotherapy (CAPEOX) — with the goal of shrinking the tumor enough to potentially save the rectum and avoid a permanent colostomy bag. **You may be eligible if...** - You are 18 or older - You have rectal adenocarcinoma where the tumor is within 5 cm of the anus - Your cancer is Stage I, II, or III - Your cancer has tested negative for a certain DNA repair defect (MSS or pMMR) - You have not yet received any cancer treatment (chemotherapy, radiation, or immunotherapy) - Your general health is good (ECOG performance status 0–1) **You may NOT be eligible if...** - You have a defect in DNA mismatch repair (dMMR/MSI-H) - You have received prior treatment for this cancer - You have certain immune conditions or serious organ problems Talk to your doctor to see if this trial is right for you.