August 5th, 2013
Deja Vu All Over Again: Study Links Calcium-Channel Blockers to Breast Cancer
A new observational study raises the possibility that calcium-channel blockers (CCBs) may be associated with a higher risk for breast cancer. Although previous studies examining this relationship have failed to turn up convincing evidence of a link, the authors of a paper published in JAMA Internal Medicine state that their study is the first to look at long-term use of CCBs in a contemporary population.
Christopher Li and colleagues analyzed data from women in the Seattle area, including 880 women with invasive ductal breast cancer, 1,027 with invasive lobular breast cancer, and 856 controls with no cancer. They found that women taking other antihypertensive drugs, including diuretics, beta-blockers, and angiotensin II antagonists, had no increased risk for breast cancer. But women taking CCBs had significantly elevated risk for ductal breast cancer (OR 2.4, CI 1.2-4.9, p=0.04) and lobular breast cancer (OR 2.6, CI 1.3-5.3, p=0.01). The results were consistent for different types of CCBs.
In an accompanying editorial, Patricia Coogan writes that the study “provides valid evidence supporting the hypothesis that long-term CCB use increases the risk of breast cancer.” As CCBS are the ninth most commonly prescribed drug class in the U.S., “the hypothesis has significant clinical and public health implications.” However, she writes, the results do not mean long-term use of CCBs should be discontinued, “because these data are from an observational study, which cannot prove causality and by itself cannot make a case for change in clinical practice.” On the other hand, the results should not “be dismissed as random noise emanating from an observational study.” She writes that “it is important that efforts be made to replicate the findings.”
One hypertension expert with very long experience in this area is Franz Messerli. In response to my questions, he noted that “there is virtually no antihypertensive drug or drug class that not has been associated with cancer at one time or another.” In particular, CCBs were at the center of a heated debate in the 1990s that was ultimately resolved by the ALLHAT trial, which found no suggestion of an increased risk of cancer associated with CCBs.
One possible source of confusion, Messerli pointed out, is that “hypertensive patients see physicians more often, particularly when their hypertension is more severe as to require CCB therapy. Frequent physician visits increase the odds of cancer diagnosis.”