For a lot of people on heavy chemo and changes of chemo, they experience some distortion and variance with their blood markers, sometimes substantially.
I've commented on using more markers and nonstandard adjuncts, as we do. My usual initial suggestions
are for newly dx'd patients with colon cancer, facing surgery before chemo.
Some of us, have seen less distortion with milder, continuous chemo formulas and selected supplement routines. My wife seems well guided with extra blood markers, smoother data, and fewer scans. Our experience with resected metastatic cancer has been that you have to keep enough chemo and immune intensity on the residual cancers to keep the markers down. Below some threshold, the markers start to sprout and we have to re-up the nonstandard (but mild) stuff (e.g. celecoxib, PSK, IV vitamin C etc). Mild, continuous oral chemo is a given, or the markers start to sprout... and they are a little harder to beat down. Also, when they sprout, the markers may shift, e.g. CEA and AFP are fine right now, but CA199 is elevated; six years ago, CA199 was the first to retreat to baseline on improved chemo where CEA was still elevated, until we got the mets cut out.