Johnson & Johnson's (NYSE: JNJ) prostate cancer treatment abiraterone works pretty well, but it won't steal sales from Dendreon's (Nasdaq: DNDN) Provenge anytime soon.

Technically, we already knew the drug worked. Johnson & Johsnson stopped a clinical trial testing abiraterone early, because it was clear the drug worked better than placebo. The only question was how much better.

Johnson & Johnson revealed the answer at this year's European Society for Medical Oncology meeting: 3.9 months better. In cancer terms, that's not bad. Patients taking abiraterone survived 14.8 months, compared to 10.9 months for patients taking placebo; a 36% increase in survival time. But the data isn't striking enough for other drugmakers to be shaking in their boots, either.

Prostate cancer patients typically start with an inhibitor of testosterone, since most prostate cancer tumors need testosterone to grow. Once the tumor stops responding -- so-called castration-resistant prostate cancer (CRPC) -- patients move on to chemotherapy, such as sanofi-aventis' (NYSE: SNY) Taxotere. Johnson & Johnson tested abiraterone in patients that had already failed both regimens, so it won't be directly competing with them.

Dendreon's Provenge is an alternative to Taxotere, so it won't be directly competing with abiraterone, either. Johnson & Johnson is testing the drug in this earlier patient population, but until the results are out, it's hard to say exactly how well it might help those patients. Even if abiraterone works well in CRPC, it might end up being more of a Provenge delayer than a Provenge killer. The drugs work through completely different mechanisms, so it's possible that Provenge would still be used once abiraterone stopped working. The two could even potentially be used in combination with each other.

Sanofi's Jevtana is approved to treat the same population in which abiraterone was tested, but it's unclear which one is the winner here. Jevtana extended survival by just 2.4 months. But Sanofi tested Jevtana against EMD Serono and OSI Pharmaceuticals' (Nasdaq: OSIP) Novantrone; Johnson & Johnson compared abiraterone to placebo, which will make the comparator look better. The absolute survival time was better for Jevtana, although it's difficult to know whether that's real or just an artifact of differences in the patients enrolled in the study. Working in abiraterone's favor, the drug seems to have a pretty mild side effect profile.

Either way, Johnson & Johnson has set the bar for new prostate cancer treatments being developed by companies such as Medivation (Nasdaq: MDVN) and OncoGenex Pharmaceuticals (Nasdaq: OGXI). If they can't beat placebo by 3.9 months, there's little chance they'll be successful.

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