@babab My surgeon and medical oncologist both essentially say the same about the meaning of the numbers. They seem to be guided by results that show detectable vs non detectable along with pet scans. My surgeon also told me that in my case there were likely not enough cancer cells to show on a cat scan. (I was upstaged to stage 3 after radical cystectomy in Jan 2024. After 4 cycles of chemo it became non detectable for about 11 months. It came back this year with a very low number 0.33 . Nothing showed on CAT scan but based on Signatera PET scan was ordered and showed uptake in pelvic nodes. 2 cycles of Padcev and Keytruda put me back to non detectable . I have PET scan and Signatera coming up after I finish cycle 6 of current treatment in next few weeks .