CEA and CA199 before the first treatment are still important data for clues along with other panels, coupled with scans and/or surgical masses.
Radiation and heavy chemo distort the blood panels during and after treatment for months, each panel with individual trajectory, but they typically trail off to a new normal. Inflammation sources (ESR, hsCRP, ferritin) , high blood sugar (FBG, HgbA1C) and hypothyroid (TSH, fT3) are potential elevation or instability problems for CEA and CA199 that we can track (with blood panels). In our case, we could control these well with low carb diet and supplements. Celecoxib and (bi)weekly IV vitamin C were heavy hitters on inflammation tests but all are important, dessicated natural thyroid for TSH. CA199 was the measurement more sensitive to "background noise" but it has worked well with supportive treatments and data panels.
zxguy is your statistical "hope case" for others persistently at CEA ~15 and over. When things got about that high, some months after a dose reduction in our case, it required mild but better chemo and major surgery to fix. The longer and higher CEA rises, the more likely medical action will be needed. I have to admit I am curious what other factors or anomalies might show up in zxguys extended bloodwork. In active cancer, usually there are patterns that can be watched and factored with multiple panels, rather than just use a nuclear alarm on one marker with a single, artificial threshold.
It is important to keep cool and take useful, calculated actions over the months that this plays out. We have found that we could target, manipulate, limit spread, and even shrink or necrose flagrantly metastatic colon cancer with additions and changes in supplements and mild drugs. Even further with a mild oral 5FU drug, of course.
I strongly believe that extra homework, started early, can gain extra chances. It is shrugs, slips, interference and pratfalls that cost us time (both ways) and money.
watchful, active caregiver for stage IVb CC since early 2010. immuno"Chemo forever," for mCRC