When deciding how best to control their high blood pressure, or hypertension, most postmenopausal women's top priority is getting and keeping their blood pressure under control. What they may not realize is that choosing certain antihypertensive medications may also increase their risk of breast cancer considerably.

Calcium channel blockers, or CCBs, a class of antihypertensive drugs, significantly increased the risk of breast cancer according to a new study. The long-term study looked at the effect of the use of antihypertensive medications on breast cancer risk in 1,763 women between the ages of 55 and 73 years.

Women taking CCBs for 10 years or longer had an approximately two and a half times higher risk of both invasive ductal and invasive lobular breast cancer than those who never used CCBs.

“Because hypertension is a chronic condition, most people with high blood pressure will often stay on their antihypertensive regimen for long periods of time,” Christopher Li, lead author on the study, told TheDoctor. He believes that learning more about the potential association between antihypertensive use and breast cancer, the most common cancer in women, is an important clinical and public health issue. Looking at this association is particularly important because people now have more options than ever for managing their hypertension.

Other classes of antihypertensive drugs include angiotensin-converting-enzyme (ACE) inhibitors (which also may pose cancer risks), angiotensin-receptor blockers (or ARBs), beta blockers, and diuretics.

Physicians sometimes prescribe combinations of these drugs, and the regimen a person is prescribed depends on their tolerance to the medication, other conditions they may have, and whether their hypertension requires a single drug or a combination of drugs to bring it under control.

The purpose of the current study was to look at the relationship between the major classes of antihypertensive drugs and the risk of the two most common types of breast cancer diagnosed in the United States: invasive ductal carcinoma, which represents about 70 percent of all breast cancers; and invasive lobular carcinoma, which represents approximately 20 percent of breast cancers.

The study's most important finding was that women taking CCBs for 10 years or longer had an approximately two and a half times higher risk of both invasive ductal and invasive lobular breast cancer than those who never used CCBs. The investigators found that even long-term use of other classes of antihypertensive drugs, including diuretics, beta blockers, and angiotensin-receptor blockers, was not associated with an increased risk of breast cancer.

Women taking CCBs should not throw away their pills just yet, however. “We do not currently think that any clinical practice should change as a result of this study,” Li said. More important is for women to continue to do those things that are already known to reduce their risk of breast cancer and get regular screenings so any cancer is detected in the early stages when it is much more treatable.

Since this is the first long-term study to look at this relationship, Li said that he and his colleagues want to see if they can replicate their findings in other study populations. “One idea would be to look in HMO-type populations, because those organizations have electronic pharmacy and medical records, and we could easily look at this question in those populations.”

The study is published online in advance of publication in JAMA Internal Medicine.