There are about 100 million prescriptions written for calcium channel blockers (CCBs) per year in the U.S. They are one of the mainstays of blood pressure control.
But a paper published in yesterday s JAMA revealed a potentially troubling development. A group from the renowned Fred Hutchinson Cancer Research Center in Seattle, reported that CCBs may be associated with a substantial increase in two types of breast cancer.
The results come from a 10-year retrospective case-control study of about 2,000 women in the Seattle metropolitan area. Although this type of study cannot definitively establish cause and effect, the magnitude of the findings will certainly raise questions about this drug class and spur further studies.
In particular, use of calcium-channel blockers for 10 or more years was associated with about a 2.5-fold increased risk of ductal breast cancer and lobular breast cancer.
There are three classes of CCBs, which, despite working by the same mechanism, are very different chemically. Nonetheless, all three classes were associated with the increased cancer risk, while other blood pressure medications (those that do not act as calcium channel blockers) showed no such effect.
ACSH s Dr. Josh Bloom comments, It is intriguing that the three types of CCBs were all associated with the increased cancer risk. Since they are chemically unrelated, this means that the effect is almost certainly due to the mechanism of calcium channel blocking rather than to any specific drug. There is no obvious explanation for this mechanism something that the authors acknowledge. He adds, this is an empirical observation, but the magnitude of the effect is large enough that it cannot be dismissed outright, despite the absence of any known biological plausibility. I m guessing that doctors are going to avoid long term use of these drugs in women, at least until more answers become available.