what exactly does Ca15-3 measure and should it show response to chemo?

[Lani]

Some oncologists don't want to measure it in those patients who are not metastatic , as it makes patients nervous and "we aren't going to do anything differently anyway" This study in patients with locally advanced breast cancer shows it can differentiate those in which a particular course of chemotherapy is not working, in order to try another and a subset of patients in whom recurrence is very likely, perhaps in order to place them into a clinical trial for something new.

As I understand it the vast majority of breast cancer cells express MUC-1 (they are looking into it as a new target of treatment)

So it is nice to know that that is the basis of the serum test and that it seems to be accurate in following breast cancer response to treatment and predictiing prognosis.