@cookercooker It's puzzling to me why your first oncologist ordered these blood tests and then did not explain the results to you. I read a report on these type of blood tests in a clinical pathology journal that my husband receives (he is a pathologist, retired) from USCAP (US and Canadian Academy of Pathology).

USCAP:

-- https://uscap.org/

The take-home answer on these is that some of these blood tests are not very reliable. For instance, the reliability (sensitivity) for the CA-15-3 is around 75%. That doesn't instill much confidence. The blood tests that are used most often are ones that you are familiar with - PSA (for prostate) and CA-125 for gynecological cancers and often administered for ovarian cancers. The article I read detailed the variance in lab procedures in processing these blood tests (liquid biopsies). Even when the numbers are elevated there can be reasons other than cancer for the elevation. So, with that, these blood tests (liquid biopsies) can be screening tools but are elevated numbers must be followed up with other testing protocols such as imaging. If you would like the resource for the article I read please let me know and I will dig it up.

Since you are getting CT scans regularly (every 6 weeks) and that imaging shows the tumors are shrinking then this is very good news.

Can you ask your current oncologist why the CA19-9 and CA15-3 would be ordered? And why your current oncologist doesn't put much emphasis on these screening blood tests?