(Updated from 7:09 a.m. EDT with new data from the study below.)

EMERYVILLE, Calif. ( TheStreet) -- Additional strong data from the phase II study of Onyx Pharmaceutical's ( ONXX) Nexavar in metastatic breast cancer patients are being presented this morning at a conference in Germany.

In first-line patients, the combination of Nexavar and Roche's Xeloda significantly extended median progression-free survival (PFS) to 7.6 months compared to PFS of 4.1 months for patients treated with Xeloda alone.

That's a 3.5-month advantage for Nexavar in first-line metastatic breast cancer patients.

For simple comparison's sake, a similar breast cancer study of Avastin plus Xeloda yielded a PFS of 8.6 months compared to PFS of 5.7 months for Xeloda alone -- a 2.9-month PFS advantage.

In second-line patients, the median PFS for Nexavar plus Xeloda was 5.7 months, compared to a PFS of 4.1 months for Xeloda alone.

The Nexavar-induced benefit in PFS was statistically significant for both first- and second-line breast cancer patients.

What does this all mean? Very strong efficacy data for Nexavar in metastatic breast cancer that is on par with, even better than, what's been previously reported with Roche's Avastin.

Recall, I wrote about the overall results from the Nexavar study on Monday, including concerns about the increased side effect profile of the drug, mainly hand-foot syndrome.

Update: More details from the Nexavar study from a biotech portfolio manager/analyst source who called me from the conference in Berlin (full disclosure: He is long Onyx):

Regarding Nexavar's side-effect profile, importantly, there was no Grade 4 hand-foot syndrome reported, only grade 3. (45% in the Nexavar-Xeloda arm compared to 13% in the Xeloda-alone arm.)

The doctor making the presentation called the hand-foot syndrome associated with Nexavar something that doctors need to pay attention to but that is "manageable."

Discontinuations due to adverse events in the study were 15% in the Nexavar-Xeloda arm compared to 7% in the Xeloda-alone arm. And only eight patients taking Nexavar discontinued due to hand-foot syndrome, vs. two patients in the Xeloda arm.

The next important Nexavar data in breast cancer should come late this year or early in 2010 from another randomized phase II study looking at the combination of Nexavar plus Taxol vs. Taxol alone. This study is key because if also positive, analysts will start to plug in breast cancer revenue into their Onyx models in a substantive way.

For now, I think Nexavar is showing a real promise in breast cancer, which would add another blockbuster indication on top of current approvals in kidney and liver cancers.

-- Reported by Adam Feuerstein in Boston
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