Johnson & Johnson released interim data from a late-stage study that showed its prostate cancer drug, Zytiga, improved survival of men with less advanced forms of the disease. The newly released data may help expand the indication of the already approved drug to treat a larger patient pool.

In the J&J study, patients with prostate cancer who had not yet received chemotherapy were treated with a combination of Zytiga and the steroid prednisone and compared to a control group taking a placebo in combination with prednisone.

Though the study was not due to be completed until 2014, an independent data monitoring panel ended the study early based on findings that showed that the Zytiga therapy delayed the growth of prostate cancer significantly as well as showing continued evidence of favorable safety.

Zytiga was first approved in April 2011 as a treatment for prostate cancer patients who had already been treated with chemotherapy. The interim data, however, could potentially open a much larger market for the drug and place Zytiga into direct competition with Dendreon’s Provenge, a prostate cancer vaccine approved by the U.S. Food and Drug Administration in April 2011.

The interim data did not show to what extent Zytiga prolongs survival, but if the twice-a-day pill works as well as or better than Provenge, Dendreon could face tough new competition. Provenge was touted as a potential blockbuster treatment before running into major reimbursement hurdles.

The effects of J&J’s announcement on Zytiga have already been felt on Wall Street. The day after the announcement, Dendreon saw its shares fall 7 percent to $10.12 while Medivation, a company developing a similar prostate cancer drug to Zytiga, saw its shares soar 13.5 percent to $72.91.

J&J is due to present its results at an upcoming meeting and plans to submit them for publication in a peer-reviewed journal. The company also has plans to use the momentum from the data monitoring panel’s backing of Zytiga to apply for regulatory approval for the new use of the drug in the United States and worldwide during the first half of this year.