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Updated with chart, new stock information.

SAN FRANCISCO ( TheStreet) -- Medivation ( MDVN) and Astellas said Thursday that treatment with their experimental prostate cancer drug MDV3100 significantly reduced the risk of death by 37% in a late-stage clinical trial.

The MDV3100 results were so positive that the study is being stopped early and men receiving placebo will be offered MDV3100 instead, the companies said.

Medivation shares are up $20, or 120%, to $36.51 in early Thursday's trading.

"We are very excited about these results and will work closely with our alliance partners at Medivation to pursue regulatory submissions in the United States, Europe and Japan," said Steven Ryder, president of Astellas Pharma Global Development.

The phase III study enrolled men with advanced prostate cancer previously treated with chemotherapy. In the interim analysis, men treated with MDV3100, a pill, reported a median survival of 18.4 months compared to 13.6 months for men treated with a placebo -- or a 4.8-month survival benefit favoring MDV3100.

Analyzed another way, the risk of a man dying of prostate cancer while being treated with MDV3100 was reduced by 37%. The results from the interim analysis were statistically significant, which is why the study was stopped early.

The MDV3100 results stack up well against Johnson & Johnson's ( JNJ) prostate cancer drug Zytiga, which demonstrated a 3.9-month survival benefit in the same prostate cancer patient population. MDV3100 and Zytiga are similar drugs and have not been tested directly against each other, but Medivation shares are soaring Thursday in part because MDV3100's efficacy appears superior to Zytiga.

Zytiga must be administered with a steroid that can cause side effects. That's another potential advantage for MDV3100, which doesn't require steroid co-administration.

Both MDV3100 and Zytiga work similarly by interfering with the way prostate cancer cells feed from testosterone produced in the body.

The stellar MDV3100 data will add Dendreon's woes and the risk that its prostate cancer therapy Provenge fades into irrelevancy. Zytiga and MDV3100 will be used initially in prostate cancer patients after they stop responding to chemotherapy, but doctors are most interested in using both drugs before chemotherapy, which is where Provenge is currently used.

The MDV3100 win is also a nice resurrection story for Medivation and its CEO David Hung following the Dimebon -- Dimebomb -- Alzheimer's blow-up. Hung has proven himself to be one of the best dealmakers in biotech, negotiating huge partnerships with Pfizer ( PFE) and Astellas, but he needed a drug development victory to gild his reputation.

On Thursday, Hung scored -- big time.

--Written by Adam Feuerstein in Boston.

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Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.

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