http://training.seer.cancer.gov/module_diagnostic/unit03_tumor_markers.html

There's a marker
C219 Presence is associated with multidrug resistance.

Can patients and/or oncologists use that to know when chemo will no longer
work?

If so, do you use it?

Also does it apply to epithelial ( most conmon) cancers?  Or all cancers?
Thanks
J