Long-term use of calcium-channel blockers may increase older women’s risk of breast cancer by more than twofold, according to a study published online Aug. 5 in JAMA Internal Medicine. If confirmed, the results may point to a modifiable risk factor in breast cancer.

Patients filled about 90 million calcium-channel blocker prescriptions in 2010, wrote Christopher Li, MD, PhD, of the Fred Hutchinson Cancer Research Center in Seattle, and colleagues. "Because hypertension is a chronic condition, most people with high blood pressure use antihypertensive drugs chronically and will often stay on the same regimen for long periods of time," he said in a release. "Characterizing their potential associations with the most common cancer in women is an important clinical and public health issue, particularly with the increasing availability of alternative options to manage hypertension."

Li et al used the Cancer Surveillance System to identify women between 55 and 74 years old in the greater Seattle area who had a diagnosis of primary invasive ductal or lobular breast cancer between 2000 and 2008. They included all women with the less common invasive lobular carcinoma (ILC) and a 25 percent sample of women with invasive ductal carcinoma (IDC) as eligible candidates for the study. They also recruited a control population.

Women who agreed to be interviewed and to participate in the study made up the final sample: 880 in the IDC group, 1,027 in the ILC group and 856 in the control group. All participants underwent interviews that addressed medical history and use of drugs such as ACE inhibitors, ARBs, beta-blockers, calcium-channel blockers, diuretics and combination antihypertensive drugs plus the duration of use. Women who never used any antihypertensive medication became the reference group.

All three groups had similar patient characteristics for age, history of hypertension, heart disease and hypercholesterolemia. Overall, use of antihypertensives was not associated with either type of breast cancer; but use of calcium-channel blockers of at least 10 years’ duration showed an increased risk for IDC (odds ratio, 2.4) and ILC (odds ratio 2.6).  

Data also suggested a reduction in breast cancer risk with long-term use of ACE inhibitors, but Li and colleagues cautioned the finding should “be interpreted cautiously.”

In an accompanying editorial, Patricia F. Coogan, ScD, of the Slone Epidemiology Center at Boston University, wrote findings from an observational study didn’t warrant discontinuing calcium channel-blocker therapy after 10 years but did deserve physicians’ attention because “this is a first-rate study.”

“If the two- to three-fold increase in risk found in this study is confirmed, long-term CCB [calcium channel-blocker] use would take its place as one of the major modifiable risk factors for breast cancer,” Coogan continued. “Thus, it is important that efforts be made to replicate the findings.”