I had colon cancer in 2016 (Stage one) in the right ascending colon and had a right hemicolectomy. Twenty lymph nodes were clear. No chemo or radiation needed.

In my annual checkup, my surgeon was telling me about a blood test that can detect a reoccurrence even before it shows up in a scan. She had a patient who had rectal cancer, and it was surgically removed. They analyze the DNA specific to your tumor and then do a blood test to look for this type of DNA in follow-ups. A year after her patient's surgery, the blood test was positive, but nothing showed up on a body scan. They were able to do chemo, and the results went back to normal. This has just become available--I do not know the name of the test. Since this test on my tumor was not available in 2016, it will not work for me. I would advise you to ask about it. Here is some information (healthline.com) that may be describing it. It is not a screen test for cancer--you have to have your tumor analyzed first and is used for checking for reoccurrence:

Doctors and scientists are working hard to identify and characterize new biomarkers for colorectal cancer. They’re also looking to improve strategies to detect and measure CRC biomarkers that have already been identified.

"In addition to what we’ve already discussed, two newer types of blood-based biomarkers for CRC are microRNA (miRNA) and long noncoding RNA (lncRNA).

miRNA: These are small strands of RNA that can play a role in controlling the types of proteins cells make. They can sometimes be found in the bloodstream. ResearchTrusted Source has documented changes in the levels of certain miRNAs in CRC compared with healthy individuals.
lncRNA: These are longer strands of RNA that can also sometimes be found in the blood. lncRNAs can also play a role in regulating how genes are expressed. A 2022 review Trusted Source notes that many lncRNAs have been associated with all stages of CRC.
Researchers are hoping to learn more about exactly how these molecules are associated with different aspects of CRC."

I would also advise you to get a second opinion, especially from a research hospital. A research hospital/center will have doctors who are also involved with the latest research on your cancer and how to treat it.