We all know that abiraterone acetate (Zytiga) plus prednisone provides a survival advantage for men with castrate resistant advanced prostate cancer (mCRPC) who have had prior treatment with a taxane based chemotherapy. New information has shown that abiraterone acetate offers a somewhat longer overall survival benefit than the data originally presented when the trial halted in 2010.
In a summary report on the MedPage Today web site it was reported that abiraterone acetate plus prednisone provided a median overall survival benefit of 4.6 months compared to a placebo plus prednisone. The final analysis of the Cougar Trial showed that, prior to any cross over from placebo to the treatment group the median survival of the men in the treatment group was 15.8 months while the placebo group plus prednisone had a median survival of 11.2 months, a 4.6 month advantage to the treatment group.
The trial also showed that the median time to biochemical progression (PSA) was 8.5 months for the treatment group vs. 6.6 months for the control group. There was also a difference in the two groups in the median time to radiologic progression (5.6 months for the treatment group vs. 3.6 for the control.
Grade 3 and 4 side effects included fatigue, anemia, back pain, and bone pain which was reported in similar frequencies in both the treatment and the control group. However, the treatment group experienced more edema, hypokalemia, and hypertension than the control group.
The survival data shows that abiraterone acetate is still not as long as the overall survival benefit offered by data of the enzalutamide trial in a comparable group of men with mCRPC. However, we do not know about the possible effect of sequencing the drugs or even combining them. Additionally, we do not know what the effect would be on either drug if they too were sequenced with treatments like Provenge.
Joel T. Nowak, M.A., M.S.W.