Women who have breast cancer and are treated with two chemotherapy drugs, anthracycline and trastuzumab, may experience more cardiac problems like heart failure than shown in previous studies, according to a new Cancer Research Network study by Group Health researchers and others in the Journal of the National Cancer Institute.

The study is important because more and more women are surviving longer with breast cancer, so it's becoming a chronic disease, said lead author Erin Aiello Bowles, MPH, an epidemiologist at Group Health Research Institute.

Breast cancer is one of the most common cancers in the United States, with an estimated 232,620 new diagnoses in 2011.  Often the cure is also problematic, as when chemotherapy causes other health problems, as shown in this study.

Bowles and colleagues estimated real-world use of anthracycline and trastuzumab use and their associations with heart failure and cardiomyopathy. Earlier clinical trials had shown that women treated for breast cancer with the drugs anthracycline or trastuzumab were at increased risk for heart failure, cardiomyopathy, or both. Like most clinical trials, the earlier clinical trials excluded large categories of patients, including elderly women and those with other health problems, such as existing heart disease. Excluding these women could make the studies miss what happens in the general population, they felt.

"We tried to take a broader look by estimating the risk of heart failure in a more general population," Ms Bowles said. "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."

In the population-based, retrospective cohort study of 12,500 women diagnosed with invasive breast cancer, the overall risk of developing either heart failure or cardiomyopathy was significantly higher in women on anthracycline alone compared with no chemotherapy, yet similar to results of previous clinical trials.

The overall risk of these cardiac problems was even greater among women who used trastuzumab alone and the risk among women who used both anthracycline and trastuzumab was greater than previously reported. Also, women receiving anthracycline — with or without trastuzumab — tended to be younger and without other illnesses; by contrast, women on trastuzumab alone tended to be older and have more illnesses. 

Chemotherapy can cause cardiac problems through several mechanisms, Ms. Bowles added. "These drugs are toxic," she said. "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."