An initial rise in CEA level during effective chemotherapy in colorectal cancer patients may not always indicate progression of disease but may be a transient CEA surge in patients responding to chemotherapy. Please see previous threads on this topic. With the advances being made in other tests the utilization of CEA, for surveillance during and after chemo is no longer preferred. A much better test is circulating tumor DNA, please ask your oncologist about CTDNA testing. For a specific cancers and stages eg colon cancer stage two or three, a more refined CTDNA test called Signatera, made from genes from your tumor, has shown excellent predictive results. I would suggest you shouldn't be so worried about CEA.