This study is for adults with locally advanced rectal cancer that has not spread to distant organs, and is classified as pMMR or MSS (which means it typically does not respond well to immunotherapy alone). The purpose is to see if a new combination of treatments given before surgery (neoadjuvant therapy) can more effectively shrink the tumor and increase the chance of curing the cancer or avoiding surgical removal of the rectum.
The main things you will do in this study are:
1. Receive a Short Course of Radiation Therapy (5 treatments over 1 week).
2. After a 1-week break, receive a combination of three drugs:
1）Nal-IRI (a special form of the chemotherapy drug Irinotecan, designed to have fewer side effects) 2）Capecitabine (a chemotherapy pill) 3）Camrelizumab (an immunotherapy drug) 3. This drug combination is given in 8 cycles, with each cycle lasting 3 weeks. 4. After finishing all cycles, the doctors will carefully check how the tumor responded.
The most important goal of this research is to see how many patients achieve a "Complete Response," which means:
1. No sign of cancer cells in the surgically removed tissue (Pathological Complete Response, pCR), or
2. No sign of cancer can be found through clinical exams, scans, and scopes, allowing the patient to avoid immediate surgery under a "Watch and Wait" strategy (Clinical Complete Response, cCR).
Researchers will also monitor:
1. The safety of the treatment and its side effects.
2. How well the cancer is controlled over time (e.g., 3-year survival without cancer recurrence).
3. The rate of successful tumor removal and the rate of preserving the anus.