PARIS ( TheStreet) --An experimental chemotherapy drug from Sanofi-Aventis ( SNY) extended significantly the survival of men who failed previous treatments for advanced prostate cancer, according to results from a phase III study disclosed Wednesday.

Sanofi plans to seek approval for the new drug known as cabazitaxel with regulatory agencies in the U.S. and Europe later this year, the company said.

If the cabazitaxel data hold up under U.S. Food and Drug Administration review, the drug will be the first approved for this indication and the only drug that's ever been shown to demonstrate a survival benefit in patients with such an advanced form of prostate cancer. (No drugs are currently approved for so-called second-line prostate cancer, so doctors treat patients today with a mix of older or experimental drugs.)

The Sanofi study of cabazitaxel enrolled 755 men with advanced prostate cancer whose tumors began growing again after first-line treatment with Taxotere, another Sanofi drug and the only chemotherapy currently approved to treat the disease.

Men treated with a combination of cabazitaxel and the steroid prednisone reported an overall median survival of 15.1 months compared to 12.7 months median overall survival for men treated with mitoxantrone, another commonly used chemotherapy, and prednisone.

Overall, treatment with cabazitaxel resulted in a 30% relative reduction in the risk of death compared to mitoxantrone. The survival benefit favoring cabazitaxel was highly, statistically significant.

"Cabazitaxel demonstrated an unequivocal improvement in overall survival," said Dr. Oliver Sartor of Tulane University's School of Medicine, a co-principal investigator in the study.

Cabazitaxel patients were more likely to experience fever with a drop in the number of infection-fighting white blood cells compared to mitoxantrone-treated patients, according to the study's safety results.

Sartor is presenting full data from the cabazitaxel study on Friday at the American Society of Clinical Oncology Genitourinary Cancers Symposium.

"I would predict FDA would look favorably on cabazitaxel, so if approved, the drug will set a new standard for prostate cancer therapy," said Sartor.

Cabazitaxel and Taxotere (known scientifically as docetaxel) both belong to the taxane class of injectable chemotherapy drugs, which work by interfering with cancer cell division. Cabazitaxel was designed specifically to overcome resistance that some patients develop to other taxanes.

In addition to prostate cancer, Sanofi is testing cabazitaxel in a number of other solid tumor studies.

Sanofi shares closed Wednesday at $37.64.

-- Reported by Adam Feuerstein in Boston.

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