Some of my posts over the last week or two have discussed the issue of the development of cross-resistance of two of our newest treatments for advanced prostate cancer.  These drugs are abiraterone (Zytiga) and enzalutamide (Xtandi).

Currently, both of them are approved for use after a man has failed chemotherapy with docetaxel. In addition, abiraterone is also approved for use prior to chemotherapy. This means if one were to strictly follow the FDA label we would all be receiving abiraterone, docetaxel and then enzalutamide.

One of the great concerns we have is whether or not taking one of these drugs before the other will dissipate the efficacy of the second drug.  In this case, will takings abiraterone cause the enzalutamide not be as effective?  The answer is very possibly!

Enzalutamide improves overall survival (OS) in men with metastatic castrate resistant prostate cancer (mCRPC) both before and after docetaxel treatment. In reality we know very little about the optimal sequencing of these drugs and the possible cross-resistance that could develop.

Being concerned about this issue a study was conducted of the biochemical response and OS after enzalutamide treatment in post-chemo mCRPC patients following progression on post-chemo abiraterone treatment.

Study involved twenty-four post-