Johnson & Johnson's  prostate cancer drug Zytiga improved survival in patients who had not received chemotherapy in a late-stage study, the company said on Thursday.

An independent data monitoring committee unanimously recommended that patients receiving a placebo in the trial be offered treatment with Zytiga, the company said.

"This news is clearly a significant positive for J&J. An approval in the pre-chemo population should more than double the market opportunity for Zytiga. We would expect physicians to increase their use of Zytiga off-label in this population once the data is released, even before official FDA approval is achieved," Bernstein Research analyst Derrick Sung wrote in a research note.

"We continue to believe that 2012 will be a seminal year for J&J's pharmaceutical franchise, as they will see four of their recently launched products (Zytiga, Xarelto, Incivo and Stelara) begin to build sales toward blockbuster status this year," he added.

The news sent shares of J&J up 1 per cent and shares of Medivation Inc, which is also developing a prostate cancer pill that works by targeting the same hormone that Zytiga targets, up almost 15 percent.

However, shares of Dendreon Corp fell about 16 per cent. Dendreon makes a prostate cancer vaccine, Provenge, that has a different mechanism of action. – Reuters