Abstract
BackgroundIn a recent case–control study, long-term use of calcium channel blocking drugs was associated with a greater-than-twofold increased breast cancer risk. If prospectively collected data confirm that calcium channel blocker use increases breast cancer risk, this would have major implications for hypertension treatment. The objective of this study was to determine whether women using calcium channel blockers for 10 years or more were at increased risk of developing breast cancer compared with women not using calcium channel blockers.MethodsThe Sister Study is a prospective volunteer cohort study of women from the USA and Puerto Rico designed to evaluate environmental and genetic risk factors for breast cancer. Beginning in 2003, women between the ages of 35 and 74 were recruited. They were eligible to participate if they had a sister with breast cancer but had not been diagnosed with breast cancer themselves. In total, 50,884 women enrolled in the cohort between 2003 and 2009; 50,757 women with relevant baseline data and available follow-up data are included in this study. The exposure of interest is current use of calcium channel blocking drugs and the reported duration of use at entry into the cohort. Secondary exposures of interest were the duration and frequency of use for all other subclasses of antihypertensive drugs. Our main outcome is a self-reported diagnosis of breast cancer during the study follow-up period. With patient permission, self-reported diagnoses were confirmed using medical records.ResultsResults showed 15,817 participants were currently using an antihypertensive drug, and 3316 women were currently using a calcium channel blocker at study baseline; 1965 women reported a breast cancer diagnosis during study follow-up. Using Cox proportional hazards modeling, we found no increased risk of breast cancer among women who had been using calcium channel blockers for 10 years or more compared with never users of calcium channel blockers (HR 0.88, 95 % CI 0.58–1.33).ConclusionsWe saw no evidence of increased risk of breast cancer from 10 years or more of current calcium channel blocker use. Our results do not support avoiding calcium channel blocking drugs in order to reduce breast cancer risk.Electronic supplementary materialThe online version of this article (doi:10.1186/s13058-016-0720-6) contains supplementary material, which is available to authorized users.
Highlights
In a recent case–control study, long-term use of calcium channel blocking drugs was associated with a greater-than-twofold increased breast cancer risk
We focused on use of calcium channel blockers that lasted for 10 years or more, because this is the length of usage that has recently been associated with breast cancer risk
After excluding women missing relevant baseline or follow-up data or who were diagnosed with breast cancer before completion of enrollment activities, we had an analytical cohort of 50,757 women for this study: 17,068 women (33.6 %) reported ever taking an antihypertensive drug in their lifetime; and 15,817 (31.2 %) were currently using an antihypertensive drug, 3316 of whom were currently using a calcium channel blocker at study baseline
Summary
In a recent case–control study, long-term use of calcium channel blocking drugs was associated with a greater-than-twofold increased breast cancer risk. A recent case–control study of women aged 55–74 reported a twofold increased risk of breast cancer for women who were current calcium channel blocker users with at least 10 years of use [1]. This increased risk was observed relative to women who had never used antihypertensive drugs, and relative to women using another type of antihypertensive for 10 years or more. Uncertainty about calcium channel blocker use and breast cancer risk remains; many of these prospective studies have been limited by small numbers of breast cancer cases, failure to examine drug subclasses, or short durations of antihypertensive use
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