Men dying from prostate cancer (search) may be able to extend their lives, thanks to a potent form of vitamin D (search) developed at Oregon Health & Science University.

A new study considered men who had advanced tumors growing despite surgery or radiation and subsequent drug treatment.

Doctors now give such patients the chemotherapy docetaxel (search), which lets them live for about 16 months, on average.

Adding the experimental vitamin pill DN-101 to that chemotherapy increased the average expectancy to roughly two years.

A two-year survival "is the highest ever seen in a randomized study," said Dr. Bruce Montgomery, a Seattle Cancer Care Alliance prostate cancer expert who was not involved in the research. "It clearly is a big step forward."

Although researchers know DN-101 added at least seven months to the average survival, they can't yet calculate the new median life expectancy, because half the men who took DN-101 in the study are still alive.

The treatment "has a lot of guys I see every day getting a meaningful chunk of extra time, without any extra side effect," said Dr. Tomasz Beer, the OHSU Cancer Institute scientist who helped develop the drug.

Such late-stage cancers kill more than 30,000 U.S. men every year, according to the American Cancer Society.

The study followed 250 men, randomly assigned to receive either docetaxel alone or with DN-101.

Among the 125 men who used the chemo drug alone, the median survival was 16.4 months. The median survival among men who also took DN-101 is an additional 7.1 months, and counting.

The 250-patient study was big enough to indicate the pills extend life, but not big enough to prove DN-101 is ready for market. That will take a study with about 600 men, Beer said.

When a larger study might start is unclear. Officials with DN-101's manufacturer, South San Francisco-based Novacea Inc., want to meet with the Food and Drug Administration before deciding how to proceed, Chief Executive Officer Brad Goodwin said.

Montgomery said the DN-101 study is part of a push to find safe medicines that make cancers more susceptible to the toxins in chemotherapy drugs.

If DN-101 makes it to market, OHSU stands to profit. The university licensed the drug to Novacea in 2002, getting payments including stock in the privately held company and royalties on any sales of the drug.