A study by the Group Health Research Institute in Seattle has determined that trastuzumab, the drug behind the brand name Herceptin, raises the risks for heart problems in breast cancer patients much more than previously thought. Trastuzumab is widely prescribed alongside chemotherapy to increase survival chances for patients with breast cancer.

Erin Bowles, an epidemiologist at the Group Health Research Institute and lead author of the study, explains that previous studies of trastuzumab and similar drugs often exclude elderly women or those with other health problems that prevent them from being part of clinical trials. However, as breast cancer treatments improve, the ages of women with breast cancer are increasing.

“We tried to take a broader look by estimating the risk of heart failure in a more general population,” said Bowles. “We looked at all the women in a population with breast cancer, not selected ones. Our study shows that people who are not generally eligible for clinical trials – older women and those with existing heart failure – do receive these drugs in real life.”

Bowles’ cohort study looked at 12,500 women diagnosed with breast cancer. It found that the overall risks of developing heart failure or cardiomyopathy when trastuzumab was taken alone are greater than chemotherapy alone. The risks of combined chemotherapy and trastuzumab are even higher.

“These drugs are toxic,” said Bowles. “They kill cancer cells, and sometimes kill other cells in the body, too. These drugs are still important for women with breast cancer to use because we know they improve survival. But as with any drug, people need to be aware of the risks, too.”