On March 4, 2014 I wrote a post “Castrate Resistant Prostate Cancer- What to Do Next” (www.advancedprostatecancer.net/?p=4425). The basic theme of the post was about how difficult it is to know how to sequence the new drugs we have to treat advanced prostate cancer (metastatic castrate resistant prostate cancer aka mCRPC).
In the post I said “There is a small trial that has shown that in many cases Xtandi will still be effective after the failure of Zytiga. I am not aware of a trial with results that has shown the efficacy of Zytiga after Xtandi (not to say that it won’t be effective).” Since I wrote that I have become aware of a very similar small trial that has demonstrated that that after failure of enzalutamide (Xtandi) abiraterone (Zytiga) will still work for some men.
In both cases there is some cross resistance, but we simply do not know the actual extent of the cross resistance nor which of these drugs might create more resistance.
Bottom line is that as of this moment we do not know which of these drugs would serve as the best first drug. There is a lot of on going research examining sequencing and combining therapies.
Until we have more data it is like the wildwest, to some extent we will have to shoot from the hip. However, we should rely on our doctors for guidance when making these decisions. This is one of the many reasons that we must make sure that our treating physicians are on the cutting edge and know as much as possible about advanced prostate cancer. This means that they specialize in treating men with advanced prostate cancer and not be general oncologists treating all cancers.
Ann Oncol. 2013 Jul;24(7):1802-7. doi: 10.1093/annonc/mdt138. Epub 2013 Apr 12.
Clinical activity of abiraterone acetate in patients with metastatic castration-resistant prostate cancer progressing after enzalutamide.
Noonan KL1, North S, Bitting RL, Armstrong AJ, Ellard SL, Chi KN.
Joel T Nowak, M.A., M.S.W.