The provocative report indicates that women over age 65 who take the blood pressure lowering medications have more than twice the risk of developing breast cancer. A higher risk of breast cancer was observed among women taking a common class of blood-pressure lowering drugs called calcium channel blockers, or CCBs. Common types of CCBs include Verapamil, Diltiazem, Nifedipine, and nonnifedipine dihydropyridines.
Women who were taking postmenopausal hormone replacement therapy with Estrogen in addition to calcium channel blockers appeared to be at greatest risk.
The researchers speculate that CCBs may encourage tumor growth and interfere with biological defenses designed to fend off invasion by cancer cells. Specifically, calcium appears to block a type of cellular "suicide" called apoptosis, which is the body's natural defense mechanism against tumor growth.
Other studies, including one conducted in the United Kingdom, have shown no significant relationship between breast cancer and calcium channel blockers, but have indicated that the risk for all cancers is higher among people taking high doses of CCBs.