August 6, 2013 — JAMA Internal Medicine has published the first-ever study to link blood-pressure drugs like Norvasc to a possible increased risk of breast cancer. Researchers warned that older women who take drugs in the “calcium channel blocker” class for a long period of time may have a 2.5-fold higher risk of breast cancer.
The conclusions of the study were based on an evaluation of women in the Seattle-Puget Sound metropolitan area. Researchers compared 856 women without cancer to 1027 women with invasive lobular breast cancer and 880 women with invasive ductal cancer. The researchers concluded:
“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 study does not prove that blood-pressure drugs increase the risk of breast cancer, but they are a concerning — especially because the drugs are the most popular prescriptions in the United States. Drugs in the “calcium channel blocker” class account for 98 million prescriptions every year.
Other types of blood-pressure drugs include “beta-blockers,” which drop blood pressure by causing the heart to beat less forcefully. “ACE” inhibitors inhibit angiotensin, which causes blood vessels to relax. Diuretics are also prescribed to reduce blood pressure by removing liquid in blood volume.
When the researchers compared calcium-channel blockers to other types of blood-pressure drugs, breast cancer was only linked to the calcium-channel blockers. The most popular drug in this class is Norvasc, which is manufactured by Pfizer Inc.