Women taking a common class of drugs to control hypertension—called calcium channel blockers—may more than double their risk for breast cancer if they continue the medication for longer than a decade.
That alarming finding, published Monday in the journal JAMA Internal Medicine, is the first time these drugs—which include verapamil, gallopamil, and fendiline—have been linked to excess breast cancer, but the researchers emphasized that it needs to be verified by other studies before any action is taken to avoid these drugs.
“We would not recommend changes in adherence to medication based on this report,” said study co-author Kathleen E. Malone, an epidemiologist at Fred Hutchinson Cancer Research Center in Seattle. “We need replication from studies using larger populations and then it may be worth discussing.”
Boston-area researchers agreed.
“The finding raises a hypothesis that should be further studied, but we’re not at the level that people should be panicking if they’re taking calcium channel blockers and getting effective management of hypertension from them,” said Patricia Coogan, a research professor of epidemiology at Boston University’s Slone Epidemiology Center.
In the study, Malone and her colleagues interviewed more than 1900 Seattle-area women diagnosed with breast cancer to determine which medications they were taking to manage chronic conditions; when compared to a control group of women who didn’t have breast cancer, the researchers found that women who were on calcium channel blockers and had been taking them for at least 10 years were more than twice as likely to have been diagnosed with breast cancer compared to the control group.
Those taking other blood pressure medications like ACE inhibitors, beta blockers, or diuretics didn’t have any increased risk of breast cancer—nor did those taking calcium channel blockers for less than a decade.
Hormone replacement therapy is one of the few drugs that have been associated with an increased breast cancer risk, said Dr. Michael Hassett, a breast oncologist at Dana-Farber Cancer Institute. While the evidence was strong enough to curtail prescribing practices for postmenopausal women, the situation is quite different for calcium channel blockers.
Unlike with HRT, “there’s a clear survival benefit to being on blood pressure medications,” Hassett said, “and some women who do well with calcium channel blockers” may have worse side effects, like dizziness or nausea, on other medications. Others may have inadequate management of their hypertension since various categories of drugs work differently to lower blood pressure.