Study Finds Link between Calcium-Channel Blockers and Breast Cancer

The first observational study of long-term antihypertensive use and breast cancer risk found that calcium-channel blockers are associated with a greater than 2-fold increase in the risk of breast cancer in postmenopausal women [JAMA Intern Med. 2013;173(17):1629-1637].

Antihypertensive drugs are the most commonly prescribed class of drugs in the United States, with 678.2 million prescriptions filled in 2010. See Table for a list of antihypertensive medications and number of prescriptions filled for each. Despite widespread and often long-term use of these agents, few studies have characterized how different classes of antihypertensives are linked to breast cancer risk. In a new study, researchers sought to evaluate the association between use of various classes of antihypertensive medications and the risks of invasive ductal cancer (IDC) and invasive lobular cancer (ILC) among postmenopausal women aged 55 to 74 years.

The large, population-based, case-control study included postmenopausal women from the Seattle-Puget Sound metropolitan area who were diagnosed as having a primary invasive breast cancer between January 2000 and December 2008. Of the participants, 880 were diagnosed with IDC, 1027 with ILC, and 856 had no cancer. The researchers conducted in-person interviews with the participants to establish detailed histories of hypertension, heart disease, and risk factors for cancer. The researchers also gathered information on the use of antihypertensive medications, including beginning and end dates of use, drug names, dose, route of administration, pattern of use, and indications. The antihypertensives included angiotensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers, beta-blockers, calcium-channel blockers, diuretics, and combination antihypertensive drugs, regardless of indication. Furthermore, the researchers classified participants into 1 of 3 groups. Current users were patients who had used antihypertensives for 6 months or longer and were still using them. Former users were patients who had used these medications for 6 months or longer but were no longer using them, and participants who had used them for <6 months were classified as short-term users. The primary end point was risk of IDC and ILC.

Overall, the findings showed that current, former, and short-term use of antihypertensives were not associated with risk of IDC or ILC. When examining duration of effects for current users, the researchers found an increased risk associated with use of calcium-channel blockers for 10 years or longer for both IDC (odds ratio [OR], 2.4; 95% confidence interval [CI], 1.2-4.9; P=.4 for trend) and ILC (OR, 2.6; 95% CI, 1.3-5.3; P=.01 for trend). This association with 10 years or longer of current calcium-channel blocker use did not vary appreciably when the results were further stratified by estrogen receptor (ER) status (ER-positive IDC: OR, 2.3; 95% CI, 1.1-4.8; ER-negative IDC: OR, 3.1; 95% CI, 1.1-8.8; and ER-positive ILC: OR, 2.6; 95% CI, 1.3-5.2). The researchers also observed a possible association between the long-term use of ACE inhibitors and reduced risks of both IDC (OR, 0.7; 95% CI, 0.5-1.2) and ILC (OR, 0.6; 95% CI, 0.4-1.0), although the risk estimate for IDC was within the limits of chance. 

“This contemporary study of postmenopausal breast cancer adds to evidence that most commonly used forms of antihypertensive agents are not related to breast cancer risk even if used for long duration,” concluded the researchers.