by ecancer reporter Janet Fricker

The novel androgen blocking agent abiraterone acetate significantly improved overall survival in men with metastatic prostate cancer resistant to hormone therapy, reported the COU-AA-301  study presented in the presidential symposium at the 35^th Annual European Society for Medical Oncology meeting in Milan (8-12 October 2010).

Since prostate cancer growth is fuelled by the male hormone testosterone, drugs that compete for the binding site on testosterone receptor proteins located on prostate cancer cells can slow tumour growth, but most cancers eventually learn to proliferate even in the absence of androgen, leading to treatment resistance.   Abiraterone acetate has been designed to inhibit production of androgen in the testes, adrenal glands and the prostate cancer tumours themselves by blocking key enzymes in the androgen biosynthesis pathway.

In the phase III double blind study,  1,195 patients with metastatic advanced prostate cancer, who had failed up to two chemotherapy regimens  (one of which contained docetaxel), were randomized to receive abiraterone acetate (1000 mg once daily) plus prednisone/prednisolone (5 mg twice daily, n=797) or placebo plus prednisone/prednisolone (n=398). The trial involved 147 sites in 13 countries.

Results show that treatment with abiraterone acetate in comparison with placebo resulted in a 35% reduction in the risk of death (HR=0.65; p<0.0001).  Furthermore it resulted in a  36% increase in median survival in comparison to placebo (14.8 months versus 10.9 months ), and time to disease progression was  10.2 months for patients taking abiraterone versus  6.6 months for those taking placebo (P<0.0001).

Patients who received abiraterone acetate also showed significant improvements in secondary endpoints including time to Prostate Specific Androgen (PSA) progression, and an increase in radiographic progression free survival.  Adverse effects of the drug included fluid retention and hypokalemia (low blood levels of potassium).

“Abiraterone acetate has the potential to meet a significant unmet need so this news will be incredibly important to prostate cancer patients and their families,” said Johann De Bono, the study presenter, from  the Institute of Cancer Research at the Royal Marsden Hospital, London.



Check back soon for an expert interview with Prof Johann De Bono on ecancertv.