HER2-positive breast cancer, which accounts for roughly 20 percent of all breast cancers, is commonly treated with Herceptin (trastuzumab) and chemotherapy. Here, participants were randomly given Herceptin, chemotherapy and a placebo or Herceptin, chemotherapy and pertuzumab.
Women receiving pertuzumab went an average of 18.5 months before experiencing a recurrence compared to 12.4 months in the control group, a 38 percent reduction in risk.
"A six-month improvement is very good," Baselga said.
Herceptin and pertuzumab both block the HER2 growth factor, which causes these types of tumors to proliferate, although the drugs bind to different parts of the HER2 protein. But, pertuzumab goes a step further and suppresses HER2 from binding to HER3 growth factor receptors.
This study was funded by F. Hoffman-La Roche and Genentech, which make pertuzumab.
Dr. Jay Brooks, chairman of hematology/oncology at Ochsner Health System in Baton Rouge, La., said the results were "intriguing" and "could potentially be very helpful in patients with two specific subsets of breast cancer."
But he also pointed out that both drugs are very expensive (possibly up to several thousand dollars a month) and are not yet approved for these specific uses.
"As these studies mature, this will be looked at by physicians around country to try to help patients," he said.
The U.S. National Cancer Institute has more on targeted therapies for breast cancer.
SOURCES: Jose Baselga, M.D., Ph.D., chief, hematology/oncology, Massachusetts General Hospital Cancer Center, Boston; Jay Brooks, M.D., chairman, hematology/oncology, Ochsner Health System, Baton Rouge, La; Dec. 7, 2011, presentation, San Antonio Breast Cancer Symposium; Dec. 8, 2011, New England Journal of Medicine
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