My husband is still in active treatment, similar situation. I've read about a recently FDA approved blood test marketed as Shield, that seems effective in detecting staged colorectal cancers. Cannot speak from experience with the test yet. I requested more information on this test from my NP last week during my annual physical & look forward to hearing back. Here are a couple of articles related to the approval. Perhaps this would be something for your family to request in addition to the CEA testing. https://www.nytimes.com/2024/07/29/health/colon-cancer-blood-test-shield.html?unlocked_article_code=1.JE4.nivx.h2fw63Hw8qDc&smid=url-share
https://www.cnn.com/2024/07/29/health/fda-colorectal-cancer-screening-blood-test/index.html
I'm uncertain what would be available to you in Iran.