Women who are currently using calcium channel blockers and have been doing so for 10 or more years are at increased risk of the two most common histologic types of breast cancer, invasive ductal carcinoma and invasive lobular carcinoma, according to a population-based case control study.
“While some studies have suggested a positive association between [calcium channel blocker] use and breast cancer risk, this is the first study to observe that long-term current use of [calcium channel blockers] in particular [is] associated with breast cancer risk,” the authors wrote in JAMA Internal Medicine.
“Overall, current, former, and short-term use of antihypertensive were not associated with risk of either [invasive ductal carcinoma] or [invasive lobular carcinoma],” reported Christopher I. Li, MD, PhD, and colleagues from Fred Hutchinson Cancer Center in Seattle. “In examining duration effects for current users, we found an increased risk only in relation to use of [calcium channel blockers] for 10 years or longer.”
An increased risk was observed for both invasive ductal carcinoma (odds ratio [OR] = 2.4, 95% confidence interval [CI] = 1.2–4.9; P = .04 for trend) and [invasive lobular carcinoma] (OR = 2.6, 95% CI = 1.3–5.3; P = .01 for trend). The relationship did not vary appreciably according to estrogen-receptor status or type of calcium channel blocker (short-acting vs long-acting, dihydropyridines vs nondihydropyridines).
The women participating in the study were aged 55 to 74 years and included 880 diagnosed with invasive ductal carcinoma, 1,027 diagnosed with invasive lobular carcinoma, and 856 controls. The women with breast cancer were “somewhat more likely to have a first-degree family history of breast cancer, to be current alcohol users, and to be current smokers,” the researchers noted.
The study found “some indication” that the current use of angiotensin converting enzyme inhibitors for 10 years or longer was associated with reduced risks of invasive ductal carcinoma and invasive lobular carcinoma. Since the authors could cite no other studies reporting this relationship, and the risk estimate for invasive ductal carcinoma “was within the limits of chance,” they advised that the finding “needs to be interpreted cautiously.” Diuretics, beta-blockers, and angiotensin II antagonists were not associated with risk.
The investigators called for further research to confirm the association between breast cancer and calcium channel blockers. They stated that quantification of the potential relationships between antihypertensive agents and breast cancer risk may aid clinical decision-making about selection of antihypertensive agents.
In an accompanying editorial, Patricia F. Coogan, ScD, of the Slone Epidemiology Center at Boston University, stated, “the data make a convincing case that the hypothesis that long-term [calcium channel blocker] use increases the risk of breast cancer is worthy of being pursued. The data are persuasive because this was a first-rate study.”
If the two- to threefold increase in breast cancer among long-term calcium channel blocker users is confirmed, long-term use of these agents “would take its place as one of the major modifiable risk factors for breast cancer,” she added. Postmonitoring surveillance of medications vis observational studies “is a crucial public health function and should now be applied to the question of long-term [calcium channel blocker] use and breast cancer risk,” she concluded. ■