Since its FDA approval in 2011 FDA abiraterone (Zytiga) has supplanted docetaxel (chemotherapy), other than perhaps Provenge, as preferred first-line treatment for metastatic castrate-resistant prostate cancer. August 2012 saw the FDA approval of enzalutamide (Xtandi) for the treatment of castrate-resistant prostate cancer after chemotherapy.

Researchers 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 Zytiga and chemotherapy. The data included some men who had participated in the Astellas/Medivation-sponsored Early Access Program.

Xtandi was administered at a dose of 160 mg daily. Men were then followed with a monthly examination which included a PSA as well as other routine blood tests.

Men were considered evaluable for PSA response if they received Xtandi for twelve weeks. A PSA decline of 30% from baseline after 12 weeks was defined as a positive 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.

Of sixty six (66) men who were treated sixty three (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. Fifty five (55) men had previously chemotherapy and thirty eight (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 period of 12.5 weeks, eighteen (29%) men had met criteria for a PSA response. Thirteen (21%) men had stable disease and thirty two (51%) men had experienced a PSA progression.

Xtandi (Enzalutamide) showed that for a significant portion of men it had positive activity in a population of men who had been heavily pretreated and become resistant to Zytiga (abiraterone) and chemotherapy (docetaxel).

2014 Genitourinary Cancers Symposium
Abstract No: 247

J Clin Oncol 32, 2014 (suppl 4; abstr 247)
Author(s): Mark Creamer Scholz, Richard Y. Lam, Jeffrey S. Turner, Khang N. Chau, Lauren K. Becker, Clifford U. Felarca; Prostate Oncology Specialists, Marina del Rey, CA

Joel T. Nowak, M.A., M.S.W.