The prostate cancer market is roaring ahead thanks to Johnson & Johnson's (NYSE: JNJ) $970 million purchase of Cougar Biotechnology. Abiraterone, the drug that Johnson & Johnson got in the deal, gained Food and Drug Administration approval yesterday.

Approval of the drug, which will be marketed as Zytiga, came considerably earlier than its PDUFA date of June 20. Ironically -- or perhaps a sign the agency loves prostate cancer drugs -- sanofi-aventis' Jevtana, which Zytiga will compete with, had a similar experience. Both drugs are approved for prostate cancer patients that have failed a round of sanofi's Taxotere.

Dendreon's (Nasdaq: DNDN) Provenge is safe for now. Provenge is approved as a first-line treatment for metastatic castration-resistant prostate cancer before chemotherapy is used. It's possible that doctors might prescribe Zytiga off-label for patients earlier in their disease progression, but they may run into resistance from insurance companies that aren't willing to pay the high price. Hospira (NYSE: HSP) launched a generic version of Taxotere last month, which insurers may require patients try before moving onto the more expensive stuff.

Johnson & Johnson's, Dendreon's, and Sanofi's biggest problem might not be competing among themselves, but the plethora of prostate cancer drugs in development. Medivation's (Nasdaq: MDVN) MDV3100 and OGX-011 from OncoGenex Pharmaceuticals (Nasdaq: OGXI) and Teva Pharmaceuticals (Nasdaq: TEVA) could both make it to market if their phase 3 trials are successful. Exelixis' (Nasdaq: EXEL) cabozantinib is farther behind, but the phase 2 data in prostate cancer patients looked good.

Roaring ahead tends to be good for patients, but not so much for those already on the market.