Some Blood Pressure Drugs Increase Breast Cancer Risk

Use of calcium-channel blockers for treatment of high blood pressure for more than 10 years can increase the risk of breast cancer for women after menopause, a new study shows.

Researchers at the Fred Hutchinson Cancer Center in Seattle found that women taking these blood pressure medications were two and a half times more likely to be diagnosed with breast cancer compared with women of the same age group who did not use calcium-channel blockers. The study results are published in JAMA Internal Medicine.

The study is the first to link the higher cancer risk with the use of calcium-channel blockers for high blood pressure treatment, according to the authors. However, more research is needed before any changes to high blood pressure treatment regimens are made. The study shows an association but did not establish a cause and effect relationship.

The researchers found a higher risk of both lobular breast cancer (P = .04 for trend) and ductal breast cancer (P = .01 for trend) among those women who took calcium-channel blockers. Both short and long-acting agents and dihydropyridines and non-dihydropyridines were associated with the risk. But, other blood pressure medications-angiotensin II antagonists, diuretics, and β-blockers were not associated with risk.

Previous studies have suggested that there is a positive link between calcium-channel blockers and risk of breast cancer, but the data is inconsistent and some of the studies were quite small or did not analyze those taking antihypertensives long-term. Four studies found a positive link with breast cancer for both calcium-channel blockers and diuretics. But, another eight studies did not find an association.

The way that calcium-channel blockers may affect breast cancer risk is not understood. One hypothesis that is not yet backed by evidence is that these agents may block apoptosis by increasing intracellular calcium levels.

The population-based case-control study included women in the Seattle-Puget Sound area. All study participants were 55 to 74 years of age. Eight hundred and eighty had invasive ductal breast cancer, 1027 had invasive lobular breast cancer and 856 women served as no-cancer controls. Risk of different types of calcium-channel blockers were assessed including for short-acting agents, long-acting agents, dihydropyridines, and non-dihydropyridines. All 1,763 women were interviewed in person to record medical history. All three groups of women had similar age, household income, history of hypertension, heart disease, and hypercholesterolemia. Of the control participants, 45% were currently on a drug to control high blood pressure and 20% have been using such a drug for 10 years of longer.

Drugs for high blood pressure are the most frequently prescribed drugs in the United States. Of the 678 million prescriptions filled in 2010, about 14.5% were for calcium-channel blockers (98 million prescriptions). Those with hypertension take these drugs long-term. “Characterizing the associations of, potential of, [calcium-channel blockers] with the most common cancer in women is an important clinical and public health issue, particularly with the increasing availability of alternative options to manage hypertension,” said Christopher Li, MD, PhD, of the division of public health sciences at the Fred Hutchinson Cancer Center, lead author of the trial.

“Quantification of the potential relationships between use of these medications and breast cancer risk has the potential to aid clinical decision making regarding selection of antihypertensive agents for patients with hypertension, as the benefits and risks of potential medications are weighed,” concluded the authors.