The study found that adding a year of Herceptin (trastuzumab) to standard chemotherapy improved overall survival by 37 percent. The addition of Herceptin also boosted 10-year overall survival rates from 75 percent to 84 percent.
And the 10-year disease-free survival rate went from 62 percent to 74 percent for those also taking Herceptin, the study found.
The women who were given Herceptin were patients with a type of breast cancer known as HER2-positive, said study author Dr. Edith Perez at the Mayo Clinic in Jacksonville, Fla.
Up to 20 percent of invasive breast cancers are HER2-positive, according to background information in the study. Too much human epidermal growth factor receptor 2 (HER2) helps breast cancer cells grow. Herceptin works by targeting HER2 proteins to stop cancer cell growth.
The study is published online Oct. 20 in the Journal of Clinical Oncology. It was supported by the U.S. National Institutes of Health and others, including Genentech, the company that makes Herceptin.
Previous research suggesting that adding Herceptin to standard chemotherapy could improve outcomes was first reported in 2005. One of those reports was updated in 2011, according to background information in the study.
In the new research, Perez's team combined the info from two of those large studies and updated the findings. The new review followed more than 4,000 women with breast cancer. Half received chemotherapy, and the other half received chemotherapy plus one year of treatment with Herceptin. The follow-up was for a median of 8.4 years.
The researchers found that adding Herceptin improved overall survival by 37 percent. The addition of Herceptin also boosted disease-free survival by 40 percent, according to the study.
The major finding of the new study, Perez said, is that "this strategy [of adding Herceptin] had long-term benefit to decrease cancer recurrence and improve survival."
The findings show not only that Herceptin works, Perez said, ''but sustainability of the benefit."
Cardiac problems have previously been linked with Herceptin, according to background information in the study. In this update, Perez found the increase in heart problems was minor with the addition of Herceptin. Heart-related deaths occurred in 0.2 percent of the Herceptin group versus 0.1 percent in women who didn't get Herceptin.
The research found a benefit to adding Herceptin in both younger and older patients. The drug also provided a benefit whether or not cancers were estrogen receptor-positive (which means the cancer uses estrogen to grow) or not, and whether or not cancer had spread to the lymph nodes.
"What this shows is there is a sustained effect on survival," said Dr. Joanne Mortimer, director of Women's Cancer Programs at the City of Hope Cancer Center, in Duarte, Calif.
With some drugs, Mortimer said, ''sometimes you see an initial response and then it goes away. This is affirmation of survival improvement with the addition of Herceptin" for those with HER-2 positive breast cancers, she said.
But, those benefits don't come without a cost. Herceptin is expensive, with a one-year course costing approximately $64,000, according to Genentech, the company that makes the drug. The company offers patient assistance for those who may have difficulty paying for the drug, according to the firm's website.
To learn more about Herceptin, visit BreastCancer.org.