An Investigational Scan (64Cu-Labeled M5A Antibody) in Combination With SOC Chemotherapy and Radiotherapy in Locally Advanced Rectal Cancer

This study is testing a special type of imaging scan using a radioactive antibody (called 64Cu-M5A) in patients with locally advanced rectal cancer. The scan may help doctors better track how the cancer is responding to standard chemotherapy and radiation therapy before surgery. Researchers want to see how well this scan works alongside existing treatments. **You may be eligible if...** - You are 18 or older - You have confirmed locally advanced rectal cancer (T3 or T4 stage) - Your cancer produces a protein called CEA - You are scheduled to receive chemotherapy and radiation therapy before surgery - You are willing to use contraception during and for 6 months after the study **You may NOT be eligible if...** - You have uncontrolled illnesses - You are pregnant or breastfeeding - You are unable or unwilling to give informed consent - You have not completed prior chemotherapy or radiation at least 2 weeks before the scan Talk to your doctor to see if this trial is right for you.