SAN FRANCISCO (

TheStreet

) -- A researcher reconfirmed Tuesday the survival benefit for

Medivation's

(MDVN)

MDV3100 in patients with advanced prostate cancer and said seizures attributed to the experimental drug came in at a low 0.6% in a late-stage clinical trial.

Medivation receiving a clean safety report for MDV3100 has been a pressing item on the agenda of biotech investors since November when the company first announced positive top-line results from a phase III study in which

MDV3100 significantly reduced the risk of prostate cancer death

by 37%.

Five of 800 patients treated with MDV3100 in the study reported seizures compared to zero seizures among placebo-treated patients, said Dr. Howard Scher of New York's Memorial Sloan-Kettering Cancer Center.

The 0.6% seizure rate attributed to MDV3100 is below the approximate 1.5% rate seen in an earlier study of the drug using higher doses and should assuage investor concerns about MDV3100's safety profile

J.P. Morgan biotech analyst Geoff Meacham counseled clients to be relieved if MDV3100's seizure rate fell to 1% or less. Likewise, Bernstein analyst Geoff Porges was expecting a seizure rate of 1-3% that slightly favored placebo over MDV3100.

Scher, the principal investigator of the MDV3100 phase III study, discussed the results with the media Tuesday on a call sponsored by the American Society of Clinical Oncology ahead of a symposium on genitourinary cancer that starts Thursday.

Medivation shares closed Tuesday at $55.41 and are up 235% since the MDV3100 results were first announced on November 2.

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 most common adverse events occurring more frequently in MDV3100 patients than the placebo group included fatigue, diarrhea and hot flashes, said Scher. Importantly, seizure was not on the list.

MDV3100 stack up well against

Johnson & Johnson's

(JNJ) - Get Report

prostate cancer drug Zytiga, which demonstrated a 3.9-month survival benefit in the same prostate cancer patient population.

MDV3100 could generate peak sales between $1 billion and $2 billion, analysts predict. Medivation and its partner

Astellas

plan to seek approval for MDV3100 in the middle of the year with drug approved and launched in early 2013.

Both MDV3100 and Zytiga work similarly by interfering with the way prostate cancer cells feed from testosterone produced in the body. The drugs have not been tested against each other but Zytiga must be administered with a steroid that can cause side effects. MDV3100 doesn't require steroid co-administration.

Zytiga and MDV3100 will be used initially in prostate cancer patients after they stop responding to chemotherapy.

MDV3100 "will be the first front-line agent used after Taxotere therapy," said Scher, indicating his preference for the drug over Zytiga.

Doctors are also interested in using both MDV3100 and Zytiga before chemotherapy, which is where

Dendreon's

(DNDN)

Provenge is currently used.

Provenge's uptake has been slowed in part because the cancer immunotherapy prolongs survival without having any measurable effect on cancer cells or the growth of tumors. MDV3100, however, helps prostate cancer patients live longer and allows doctors to more easily assess the drug's clinical benefit.

In the study, treatment with MDV3100 significantly slowed the progression of prostate cancer spreading to the bone by 8.3 months compared to 2.9 months for placebo. Almost 30% of patients had a complete or partial response to MDV3100 compared to 1.3% for placebo-treated patients.

More than half the men in the study treated with MDV3100 had a greater than 50% reduction in their PSA level, which is used as a biological marker for prostate cancer progression. By comparison, only 1.5% of men treated with a placebo saw their PSA levels decline by 50% or more.

--Written by Adam Feuerstein in Boston.

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