Two drugs significantly extend the time that women with advanced breast cancer can live without their tumors growing, potentially changing the landscape for 80 percent of patients with the disease, according to two separate studies released Wednesday.

In each study, drugs targeting the molecular machinery in tumor growth were added to standard therapy to help keep metastatic breast cancer at bay. The results point to an important emerging strategy that attacks cancers on multiple fronts with a combination of therapies. But adding more drugs to these regimens is expected to increase the already enormous costs of treating cancer.

The two new drugs, coming on the heels of the disappointing withdrawal of Avastin's approval for advanced breast cancer, offer renewed hope that women will have more tools to fight metastatic disease, according to trial leaders and scientists not directly involved in the studies.

More than 160,000 American women have metastatic breast cancer, according to patient advocacy group Metastatic Breast Cancer Network. The disease is currently considered incurable.

One drug, called pertuzumab, extended survival without tumor growth by 6.1 months when added to the blockbuster breast cancer medicine Herceptin and chemotherapy, compared with Herceptin and chemotherapy alone. The study, sponsored by pertuzumab's developer, Roche and its Genentech unit, involved 808 patients diagnosed with so-called HER2-positive breast cancer who had not been previously treated for the disease.

The second drug, marketed as Afinitor by Novartis for other cancers, increased survival without tumor growth by 4.2 months when added to a drug called exemestane that blocks production of the hormone estrogen, compared with the hormone therapy alone.

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