Postmenopausal women who use a type of blood pressure-lowering medication called a calcium channel blocker may have increased odds of developing breast cancer, new research suggests.
Long-time users of these drugs have more than double the risk for getting breast cancer compared to women not using the medications, according to the study, published Aug. 5 in JAMA Internal Medicine.
"We looked at these drugs because people who use them to manage their blood pressure are usually on them for the rest of their lives," said the study's lead author, Dr. Christopher Li, of the Fred Hutchinson Cancer Research Center in Seattle. "There has been some evidence suggesting that some of these antihypertensives may be related to breast cancer risk."
The study of nearly 3,000 women found that among high blood pressure drugs, only calcium channel blockers carry the heightened breast cancer risk, Li said.
Drugs to control high blood pressure are the most commonly prescribed type of medication in the United States, according to the study. Channel blockers alone accounted for 98 million prescriptions filled in 2010.
Despite the potential for concern raised by this study, the findings don't warrant any modifications of clinical practice, Li said. "We have to see replication of this work before we would recommend any sorts of changes," he added.
Also, Li cautioned that the findings show an association between calcium channel blockers and breast cancer, but do not prove that they cause breast cancer.
"We need to see confirmation of these results before we make any recommendation for women to change what they are using," he said.
Channel blockers include amlodipine (Norvasc), diltiazem (Cardizem LA, Tiazac), isradipine (DynaCirc CR), nicardipine (Cardene SR), nifedipine (Procardia, Procardia XL, Adalat CC), nisoldipine (Sular), and verapamil (Calan, Verelan, Covera-PM).
Patricia Coogan, author of an accompanying editorial in the journal, agreed that this study shouldn't lead women to stop taking these drugs.
"This was a good study, but it doesn't mean doctors should stop prescribing calcium channel blockers, because it is an observational study," said Coogan, a research professor at the Slone Epidemiology Center at Boston University.
"I don't think women should be concerned yet," Coogan added. "These findings need to be replicated before anything in clinical practice is undertaken."
For the study, Li's team collected data on nearly 2,000 women with breast cancer who were between the ages of 55 and 74, and compared that with information on more than 800 women without cancer.
The researchers looked for any blood pressure medication taken, the type of medication and how long it was taken.
Women who used calcium channel blockers for more than 10 years had a 2.5-fold increased risk of developing breast cancer compared with women not taking these drugs, the researchers concluded.
The reason for the association between calcium channel blockers and breast cancer is unclear, Li said.
Other blood pressure medications, such as diuretics, beta-blockers and angiotensin II antagonists, were not associated with increased breast cancer risk in the study.