This study is about testing two blood tests for early signs of colorectal cancer (CRC) coming back after surgery. **Minimal Residual Disease (MRD) tests** like Haystack and Signatera® look for tiny bits of cancer that might be left after treatment. The Haystack test is newer and might find cancer sooner than Signatera®. **Key Points**: - **What to Expect**: You will provide blood samples before surgery, 3-10 weeks after, every 3 months for 2 years, then every 6 months for 3 more years. - **Participation**: You must be 18 or older, have stage II-IV CRC, and can have surgery to remove the cancer. - **Testing Details**: You'll be part of an MRD surveillance, which may detect cancer earlier, potentially aiding in better treatment outcomes. The aim is to see if Haystack is better at finding cancer coming back than Signatera®. Early detection can help doctors treat cancer sooner. Participants give blood samples several times over 5 years, and these tests might improve the chances of curing cancer. Eligibility includes being able to provide blood samples and having tissue samples for testing.