Circulating Tumour DNA Based Decision for Adjuvant Treatment in Colon Cancer Stage II Evaluation

This trial studies whether a blood test that detects tumor DNA (ctDNA) can guide decisions about whether people with Stage II colon cancer need chemotherapy after surgery, potentially sparing some patients from unnecessary treatment. **You may be eligible if...** - You have had surgery for Stage II colon cancer (or Stage II rectal cancer in the upper rectum) - Your microsatellite or mismatch repair status is known - Your ctDNA result is available - You have signed informed consent for both the screening and randomized phases **You may NOT be eligible if...** - Your cancer is microsatellite instability-high (MSI-H) or mismatch repair-deficient (dMMR) - You have a known reason to definitely need chemotherapy - You have a condition that makes chemotherapy unsafe - Your cancer was not completely removed (R1 or R2 status) Talk to your doctor to see if this trial is right for you.