NEW BRUNSWICK, N.J. ( TheStreet) -- Advanced prostate cancer patients that no longer respond to chemotherapy survived about four months longer after treatment with Johnson & Johnson's ( JNJ) experimental drug abiraterone compared to similar patients treated with a placebo, according to data from a phase III study presented Monday.

Johnson & Johnson announced top-line results from the positive study of abiraterone last month and said it was evaluating plans to seek the drug's approval. Detailed data, including the extent of abiraterone's survival benefit, were presented for the first time today at the European Society of Medical Oncology (ESMO) annual meeting.

The phase III study enrolled 1,195 prostate cancer patients, randomizing them to treatment with abiraterone plus the steroid prednisone or a placebo plus prednisone. All the patients in the study were diagnosed with advanced, metastatic prostate cancer whose tumors were no longer responding to hormonal therapy or chemotherapy, most notably the commonly used drug Taxotere.

Patients treated with abiraterone had a 35% reduction in the risk of death compared to patients treated with a placebo. The median overall survival in the abiraterone-treated patients was 14.8 months compared to 10.9 months for placebo patients -- a difference of just under four months favoring abiraterone.

Abiraterone works by inhibiting the production of testosterone. Prostate cancer cells both produce testosterone and feed on testosterone produced in other parts of the body. Doctors typically treat prostate cancer patients initially with hormonal therapy to stop testosterone production and slow tumor growth, but most prostate cancers become resistant to these treatments and start to grow again.

The study presented Monday used abiraterone in patients with prostate cancer that no longer responds to hormone therapy and chemotherapy -- so-called third-line patients. Johnson & Johnson is also studying the use of abiraterone earlier in patients who no longer respond to initial hormone therapy but who have not yet advanced to chemotherapy. These are similar patients to those eligible to receive Dendreon's ( DNDN) prostate cancer therapy Provenge.

Abiraterone's initial competition is likely to come from Sanofi-Aventis' ( SNY) Jevtana, approved earlier this year for third-line prostate cancer patients. In its pivotal phase III study, Jevtana showed a median overall survival of 15.1 months for patients treated compared to 12.7 months for patients treated with another chemotherapy drug mitoxantrone.

Medivation ( MDVN) and partner Astellas are developing MDV3100, a prostate cancer drug that works in a very similar way to abiraterone. Phase III studies are underway.

--Written by Adam Feuerstein in Boston.

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Adam Feuerstein writes regularly for TheStreet.com. In keeping with TSC's editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet.com. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.

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