Enzalutamide in men with prostate cancer resistant to docetaxel and abiraterone.

247 Background: Since FDA approval in 2011, abiraterone (Zytiga) has supplanted docetaxel as preferred first-line treatment for metastatic castrate-resistant prostate cancer. In August 2012 enzalutamide (Xtandi) was FDA-approved for the treatment of castrate-resistant prostate cancer after docetaxel (Taxotere). We performed a retrospective chart review at a large medical oncology clinic specializing in prostate cancer to determine the PSA response rates of enzalutamide administered to men who had previously progressed on both abiraterone and docetaxel. This report includes some patients who participated in the Astellas/Medivation-sponsored Early Access Program; however, it represents the author’s independent clinical experience. Methods: Enzalutamide was administered at a dose of 160 mg daily. Patients were subsequently followed with monthly physical examination, PSA and routine blood tests. No hepatotoxicity or seizures occurred. Men were considered evaluable for PSA response if they received enzalutamide for twelve weeks. A PSA decline of 30% from baseline after 12 weeks was defined as a response. A PSA increase of 30% from baseline within 12 weeks was defined as disease progression. Men with neither a 30% increase nor a 30% decline were classified as having stable disease. Results: 66 men were treated and 63 were evaluable for PSA response. Median age was 67. Median baseline PSA was 68.5. All participants had disease that had progressed on abiraterone. 55 men received previous docetaxel. 38 had received previous Provenge. Two men stopped before 12 weeks because of intolerable fatigue. One man died of progressive disease before 12 weeks. After a median follow up of 12.5 weeks, 18(29%) men met criteria for PSA response. 13(21%) men had stable disease and 32(51%) men had PSA progression. Conclusions: Enzalutamide has activity in a heavily pretreated population of men resistant to abiraterone and docetaxel.