Application and Exploration of Personalized ctDNA-MRD Detection Technology in Predicting the Efficacy of Neoadjuvant Therapy for Rectal Cancer

This study is testing whether a blood test that detects circulating tumor DNA (ctDNA) — tiny fragments of cancer DNA released into the bloodstream — can accurately predict how well neoadjuvant (pre-surgery) treatment is working in people with rectal cancer. The test could help doctors adjust treatment plans before surgery. This is an observational study — it does not change your treatment. **You may be eligible if...** - You are 18 to 75 years old - You have been diagnosed with rectal adenocarcinoma (rectal cancer) confirmed by biopsy - Your cancer is clinical stage II or III on MRI - Your tumor is in the lower rectum (within 10cm of the anal opening) - Your cancer can be surgically removed - You have not yet received any cancer treatment (no prior chemo, radiation, or surgery for this cancer) **You may NOT be eligible if...** - You have already received treatment for rectal cancer - Your cancer is not surgically removable - You have serious organ problems that prevent standard treatment - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.