Long-Term Current Use of Calcium Channel Blockers Is Associated With Higher Risk of Breast Cancer  

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Long-term use of a calcium channel blocker to treat hypertension is associated with higher breast cancer risk, according to a report published online by JAMA Internal Medicine. Researchers evaluated associations between various classes of hypertensives, the most commonly prescribed class of medication in the United States, and the two most common histologic types of breast cancer, invasive ductal and invasive lobular breast cancer, but only found an association for calcium channel blockers. Other antihypertensive medications—diuretics, beta-blockers, and angiotensin II antagonists—were not associated with increased breast cancer risk.

The population-based study in the three-county Seattle–Puget Sound metropolitan area included women aged 55 to 74 years, 880 with invasive ductal breast cancer, 1,027 with invasive lobular breast cancer, and 856 who did not have cancer and served as controls. 

Those who were currently using calcium channel blockers and had done so for 10 or more years had higher risks of ductal breast cancer (odds ratio [OR] = 2.4, P = .04 for trend) and lobular breast cancer (OR = 2.6, P = .01 for trend). These associations did not vary according to estrogen receptor status. In addition, the relationship did not vary much based on the type of calcium channel blockers used (short-acting vs long-acting or dihydropyridines vs non-dihydropyridines).

First Study to Find Link

“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 are associated with breast cancer risk. Additional research is needed to confirm this finding and to evaluate potential underlying biological mechanisms,” the researchers concluded. 

“Given these results, should the use of [calcium channel blockers] be discontinued once a patient has taken them for 9.9 years? The answer is no, because these data are from an observational study, which cannot prove causality and by itself cannot make a case for change in clinical practice,” Patricia F. Coogan, ScD, of the Slone Epidemiology Center at Boston University wrote in an accompanying commentary. “Should the results be dismissed as random noise emanating from an observational study? The answer is no, because the data make a convincing case that the hypothesis that long-term [calcium channel blockers] use increases the risk of breast cancer is worthy of being pursued,” she continued. 

“In conclusion, the present study provides valid evidence supporting the hypothesis that long-term [calcium channel blocker] use increases the risk of breast cancer. If true, the hypothesis has significant clinical and public health implications.… If the 2- to 3-fold increase in risk found in this study is confirmed, long-term [calcium channel blocker] use would take its place as one of the major modifiable risk factors for breast cancer. Thus it is important that efforts be made to replicate the findings.” ■

Li CI, et al: JAMA Internal Medicine. August 5 (early release online).
Coogan PF, JAMA Internal Medicine. August 5 (early release online).