CHICAGO ( TheStreet) --Treatment with Roche's ( RHHBY) Avastin helps women with ovarian cancer extend the time before their disease worsens but as of yet, the blockbuster drug has not definitively prolonged overall survival.

Results from two phase III studies of Avastin in ovarian cancer were released Saturday at the American Society of Clinical Oncology (ASCO) annual meeting. Roche has already filed Avastin for European approval in ovarian cancer. Genentech, Roche's U.S.-based arm, intends to seek U.S. approval for the drug before the end of 2011.

Avastin is widely used to treat a variety of cancers and sales totaled amost $8 billion last year, but investors have been concerned about future growth given efforts by regulators to rescind approval for use of the drug in breast cancer. Roche is fighting those efforts but the outcome is still uncertain, all of which makes approval and use of the drug in ovarian cancer more important to the company.

In the first phase III study, dubbed OCEANS, the use of Avastin in combination with chemotherapy in women with recurrent ovarian cancer reduced the risk of disease progression by 52% compared to treatment with chemotherapy alone.

"Women taking bevacizumab Avastin lived for longer periods without disease progression and without having to go back on chemotherapy," said Dr. Carol Aghajanian of Memorial Sloan-Kettering Cancer Center in New York. "This is good news for women with these cancers, as we are increasingly able to treat ovarian cancer as a chronic disease."

After two years of follow up, the median progression-free survival for women treated with Avastin and chemotherapy was 12.4 months, compared to 8.4 months for women treated with chemotherapy alone.

In addition, 79% of women treated with Avastin-chemo reported significant tumor shrinkage, compared to 57% treated with chemo alone. The duration of response (how long the tumor shrinkage lasted) was also longer for the patients in the Avastin group (10.4 months versus 7.4 months).

In the early analysis of overall survival of the OCEANS study, women receiving Avastin plus chemotherapy lived 35.5 months compared to 29.9 months in women who received chemotherapy alone. That's a trend favoring Avastin but not yet statistically significant.

In a second phase III study, dubbed ICON7, involving women with newly diagnosed ovarian cancer, Roche/Genentech reported Saturday for the first time that treatment with Avastin resulted in a 15% reduction in the risk of death.

This survival benefit, while trending in Avastin's favor, is not yet statistically significant. At a median of 28 months follow up, 178 women treated with Avastin and chemotherapy in the study had died compared to 200 women treated with chemotherapy alone. Roche intends to continue following the patients in this study for overall survival and a final analysis will be conducted after 715 deaths have occurred.

"It's too early to reach firm conclusions about the full extent of the overall survival benefit of adding bevacizumab Avastin to the treatment regimen for newly diagnosed ovarian cancer, but it does seem very promising, particularly for patients at high risk of recurrence," said Dr. Gunnar Kristensen an investigator in the study from the Norwegian Radium Hospital in Oslo, Norway.

At a previous medical meeting, researchers reported that treatment with Avastin and chemotherapy extended the time before tumors progressed compared to chemotherapy alone -- achieving the study's primary endpoint.

Genentech intends to seek approval for Avastin in ovarian cancer later this year, pending discussions with the U.S. Food and Drug Administration over how much survival data will be necessary before the drug can be reviewed and potentially approved, said Genentech spokesperson Krysta Pellegrino.

Several other companies are presenting data on ovarian cancer drugs at this year's ASCO meeting, including Exelixis ( EXEL), Nektar Therapeutics ( NKTR) and Endocyte ( ECYT).

--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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