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Lapatinib plus trastuzumab are significantly better than lapatinib alone in extending the lives of breast cancer patients whose tumors are HER2-positive, according to Kimberly Blackwell, MD, associate professor of medicine at Duke University Medical Center.

Blackwell presented the findings today at the CTRC-AACR San Antonio Breast Cancer Symposium.

Blackwell says the combination-targeted therapy gave patients more than a four-month survival advantage over those who took lapatinib alone. She says the findings may be the first step toward a chemotherapy-free future.

"This is the first time that a pair of targeted therapies has been shown to be superior to any intervention that paired a targeted therapy with a hormonal or chemotherapy based approach," she said.

The results stem from a large, Phase III clinical trial where investigators randomized 296 patients with metastatic breast cancer to receive either lapatinib (also known as Tykerb) alone or lapatinib plus trastuzumab (Herceptin) once a day.

All participants had metastatic disease that had continued to spread even after treatments with several interventions that included trastuzumab plus chemotherapy.

Blackwell says trastuzumab binds to and blocks part of the HER2 growth factor that appears on the surface of some breast cancer cells while lapatinib binds to a second growth factor, EGFR, and part of HER2 that sits below the cell surface. "It's sort of a double whammy, disabling the HER2 protein in two places instead of one."

Women who enrolled in the single-agent arm of the study and whose cancer continued to spread after four weeks were allowed to cross over to the other arm of the study to continue on the combined approach.

Fifty-two percent of the women enrolled in the lapatinib-only arm of the study crossed over to the combination arm. The median overall survival following treatment with lapatinib plus trastuzumab was 60.7 weeks compared to 41.4 weeks for those who took only lapatinib.   

Other researchers involved in the study include Hal Burstein, from the Dana Farber Cancer Institute; George Sledge, from Indiana University Cancer Center; Steven Stein, Catherine Ellis, and Michelle Casey, of GlaxoSmithKline; Jose Baselga, of Vall d’Hebron University Hospital, Barcelona, Spain; and Joyce O’Shaughnessy from Baylor Sammons Cancer Center, Texas Oncology, PA, US Oncology, Dallas.