In the near future we should be seeing more non-invasive methods to evaluate if a man is responding to their drugs.
One such example is the blood bio-marker available only at Johns Hopkins, the Androgen Receptor Variant 7 (AR-V7). Evaluating the presence of the antibody AR-V7 in the blood strongly indicates whether or not both abiraterone acetate (Zytiga) and enzalutamide (Xtandi) are demonstrating efficacy (working).
The hitch is that this blood test is available only at Johns Hopkins in Baltimore, Maryland. If you are trying to determine if your enzalutamide or abiraterone is working by having this test you can find out if you are eligible by contacting Katie Beierl (firstname.lastname@example.org. You should also confirm if your insurance company will cover the cost of the test, as many do not. If you do decide to have the test you can arrange to have the blood drawn locally and then sent to Johns Hopkins. You can also find out more about this procedure from Ms. Beierl.