Monitoring a single marker's response is incomplete biological information and misses what is happening with other markers. The various markers will actually shift dominance under an incomplete chemo tx. The shift phemomena and the divergence between scans and the solo CEA marker has been more recognized here with the Eribtux only tx, but it applies to 5FU based formulas too. Non-specific markers like LDH, GGT and quantitative d-dimer help extend coverage beyond the cancer marker antibodies. I view a single marker response as a positive start, a
partial formula, but reversing or flattening
all of the markers is part of our
criterion of adequate chemo, or combined treatment. (surgery can remove isolated resistant cells, too)
To me, "CEA only" monitoring is like driving colorblind with 20/100 vision, with one eye closed. They can drive on easy, deserted streets but no one is surprised by wrecks when driving gets tricky. A few papers demonstrate using multiple markers for CRC. IMO, good, comprehensive marker programs
should start at dx, especially before the first treatment/surgery, but can started later, faster with 1.5-3 week spacing for the first few points if not impacted by the chemo schedule.