6 months ago, I had a colon cancer surgery. After seeing the MSI report, doctor is advised me chemotherapy is not required. After my surgery I have a routine 3 months checkup, after my surgery I had 2 CEA tests where it showed 0.0 ng/ml. Today I took my CEA test, the third one after my surgery and showed 0.8 ng/ml. Could you please explain this? Thanks and regards. Ramanathan.