After following breast cancer patients for an average of 8-plus years, researchers say that adding trastuzumab (Herceptin) to chemotherapy significantly improved the overall and disease-free survival of women with early stage HER2-positive breast cancer.

They found that the use of trastuzumab produced a 37% improvement in survival and a 40% reduction in risk of cancer occurrence, compared with patients who received chemotherapy alone.

These findings, published in the Journal of Clinical Oncology (2014; doi:10.1200/JCO.2014.55.5730), demonstrate how important trastuzumab has been to the treatment of this form of breast cancer, said the study’s lead author, Edith A. Perez, MD, deputy director at large, Mayo Clinic Cancer Center and director of the Breast Cancer Translational Genomics Program at Mayo Clinic in Jacksonville, Florida.

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“This long follow-up of patients shows that we have really altered the natural history of this disease,” said Perez. “Herceptin works, and it works for a long period of time. The drug has impacted the lives of many women in the US and worldwide.”

HER2-positive breast cancer accounts for 15% to 20% of invasive breast cancers. Before the development of trastuzumab, women with early stage breast cancer that was HER2-positive faced a worse prognosis than those with HER2-negative breast cancer, including quicker relapse, higher incidence of metastasis, and shorter survival, according to Perez.

The study reports long term findings from two randomized phase III studies that led to US Food and Drug Administration approval of Herceptin use in early stage HER2-positive breast cancer. The studies were N9831, led by the North Central Cancer Treatment Group (NCCTG) Alliance, and NRG B-31, led by the National Surgical Adjuvant Breast and Bowel Project.

A combined 4,046 patients were enrolled in the studies, which tested the addition of trastuzumab to chemotherapy after surgery. All patients received doxorubicin plus cyclophosphamide, and then half received paclitaxel with trastuzumab and the other half were treated with paclitaxel alone.

The improvement in overall and disease-free survival was seen in all subgroups, including older and younger patients, patients with node-positive and node-negative cancers, as well as estrogen-positive and estrogen-negative cancers.

The findings also confirmed long-term safety of trastuzumab, Perez said. Over 8 years, there was no increase in the incidence of secondary cancers and only a minor increase in heart problems, she said.

The regimen using trastuzumab is the standard of care for early stage HER2-positive breast cancer. Trastuzumab was first tested in metastatic HER2-positive breast cancer and also showed significant benefit.

Researchers from institutes nationwide contributed to the study, which was funded by the National Institutes of Health, the National Surgical Adjuvant Breast and Bowel Project, the Breast Cancer Foundation, and Genentech.