@nldan, I can imagine that doubling CEA levels is worrisome for you and your friend. I'm glad that her care team is continuing to investigate. I did a bit of searching around because I was curious about this. As you probably know CEA testing is notorious for false positives, meaning that the test results may show high levels when they are actually not. That's why a single CEA is never enough information, they track levels over time to watch for trends.

Here's more info:
- High False-Positive Rate of Elevated CEA Seen in Patients With Resected Colorectal Cancer https://www.ascopost.com/issues/august-15-2014/high-false-positive-rate-of-elevated-cea-seen-in-patients-with-resected-colorectal-cancer/

I also found this case study, where a patient had successful treatment for colon cancer and elevated CEA levels were caused by a second cancer of the thyroid.
- High CEA levels in a case of resected colorectal cancer: delayed diagnosis of metachronous medullary thyroid cancer https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5747095/

@gaylemol, I too wonder if you were ever able to discover the reason for your rising CEA levels.
@revcindy, how are you doing? Have you returned to work?