Massive study finds no link between antihypertensive class and malignancy.

A long-simmering controversy over long-term use of calcium channel blockers to control high blood pressure and the effect that has on development of breast cancer may be settled, with researchers here reporting there is no link.

An adjusted hazard ratio for breast cancer among 107,337 women on calcium channel blockers was 0.96 when compared with 165,815 women not taking these agents (95% CI 0.90-1.03), a nonsignificant difference, said Sara Soldera, MD, a medical oncology fellow at McGill University Health Center, Montreal.

Soldera and colleagues accessed the United Kingdom Clinical Research Datalink and included women enrolled in that database from 1995 to 2009 and then followed through the end of 2010. In that time period, 3,002 women who were not taking calcium channel blockers developed breast cancer over 1,075,336 person-years compared with 1,512 cases among the women whose records indicated treatment with this class of antihypertensive drug, over 491,768 person-years.

Soldera said that there had been a controversy over whether calcium channel blockers have an impact on breast cancer. “I got the idea to do the study when some of my patients brought up the question. I think that when a women is diagnosed with breast cancer, they look back to see if there is something that might have caused it,” Soldera said. “And they ask whether it was the calcium channel blockers.”

So she hit the medical literature books and “when I researched it, there was a lot of disparity — a lot of papers saying yes, and a lot of papers saying no. But these studies had small sample sizes and poor methodology.

“So we decided to do a larger study,” she said. “We thought that with the numbers of patients and patient-years in this study, if there was a signal, we would find it. We hoped that we could kind of settle the question with this study.”

Soldera noted that many women who develop breast cancer are overweight and may be taking calcium channel blockers to combat hypertension. She suggested they can be assured that taking the medication will help control blood pressure, but won’t be causative for breast cancer.

Tufia Haddad, MD, assistant professor of oncology at the Mayo School of Medicine, Rochester, Minn., told MedPage Today, “There has not been much discussion in the community of the possible link between calcium channel blockers and risk of breast cancer given that the study results to date have yielded such mixed results.

“There have been a number of small cohort or case-control studies evaluating this possible association, and some study results have suggested there is a possible association between usage and increased breast cancer risk while other study results suggest there is no association,” Haddad said.

“A recent meta-analysis of 17 studies evaluating this association did not find an increase in breast cancer risk between calcium channel blockers users and non-users. However, in subgroup analysis, long-term use — greater than 10 years of calcium channel blockers — [was] associated with an increase in breast cancer risk. That meta-analysis evaluated the data of approximately 150,000 women of whom over 53,000 were calcium channel blocker users,” she said.

“The current abstract is a well-designed, population-based cohort study of about 270,000 women who were newly started on an antihypertensive medication,” she said.

“Regardless of type of calcium channel blocker prescribed, long- or short-acting formulation of calcium channel blocker, or duration of calcium channel blocker use, there was no observed increase in the risk of breast cancer,” Haddad said. “The results were adjusted for other important breast cancer risk factors, and there was good long-term follow-up of these patients — more than 1.5 million person years.

“So there are no consistent data to support an association between calcium channel blocker use and breast cancer risk,” she said. “The negative findings of this contemporary, large, population-based cohort study are in agreement with that.”

Soldera, in her study, found that the hazard ratio of taking calcium channel blockers for less than 5 years was 0.96; the risk or taking the anti-hypertensive for 5 to10 years was 1.05, and the risk for taking calcium channel blockers for 10 or more years was 0.61 — but in none of these calculations was the finding statistically significant.