Do Calcium Channel Blockers Increase the Risk of Breast Cancer?

A recent meta-analysis published in the journal Plos One indicates a potential link between breast cancer and use of a common blood pressure medication, but a closer look tells a different story.

Researchers in Shanghai, China, performed a meta-analysis of 17 observational studies analyzing the risk of breast cancer in patients taking several types of calcium channel blockers (CCBs), a common class of medications used to control blood pressure levels.

To calculate the relative risk of breast cancer in CCB users, Wen et al analyzed data from qualifying studies collected from several databases including PubMed, MEDLINE, EMBASE, and the Cochrane Library. These studies encompassed data from a total population of 149,607 females, and 53,812 women who used CCBs over a period of 2 to 16 years.

Some studies involved in the analysis were observational, meaning that healthy patients were monitored for new cases of breast cancer over time. Other studies were case-control studies, in which groups patients who had developed breast cancer were compared with patients who had not developed breast cancer.

Meta-analysis investigators analyzed data in several different ways, examining cohort studies and case-control studies. Neither of these analyses showed significant results for increases in the risk of breast cancer. Patients were then analyzed by the number of years of CCB use. Among patients with current use, a less than 5-year history of use, a greater than 5-year history of use, and use at any point in a lifetime, analysis showed no significant increase in the risk of breast cancer.

Finally, having performed all of these analyses, investigators limited data analyzed to studies of 10 years' duration or more. In this case, the investigators finally found a result that qualifies as statistically significant, with a hazard ratio for development of breast cancer of 1.71 (95% CI: 1.01 to 2.42) in women with more than 10 years of CCB use.

Importantly, these results were barely significant, at just under the 5% significance level. In addition, the large number of analyses conducted on the same data and the lack of statistical adjustment for multiple statistical tests limits the clinical relevance of this finding.

It is notable that among patients using nifedipine, the risk of developing breast cancer was not significantly affected, with a hazard ratio of 1.10 (95% CI: 0.87 to 1.33). Likewise, no significant increase in risk was observed with diltiazem, with a hazard ratio of 0.75 (95% CI: 0.40 to 1.10).

Instruct patients who are taking calcium channel blockers to continue taking their medications, despite news reports that may raise concerns about CCBs. The results of this meta-analysis fall under the purview of hypothesis-generating studies, and could have a harmful effect on patients with high blood pressure.

Reference:

• Li W, Shi Q, Wang W, Liu J, Li Q, Hou F. Calcium Channel Blockers and Risk of Breast Cancer: A Meta-Analysis of 17 Observational Studies. PLoS One. 2014;9(9):e105801.