A new analysis linking some calcium channel blockers to an increased risk of breast cancer in older women appears in the October 15 issue of the journal Cancer. According to the study, postmenopausal women who took calcium channel blockers had twice the risk of developing breast cancer than other women. The overall cancer risk was not increased.
Calcium channel blockers are used to treat high blood pressure and heart disease. No association was found between other high blood pressure medications and breast cancer risk.
The analysis relates primarily to short-acting calcium channel blockers and not the longer-acting variety taken by most Americans. Longer-acting varieties have a slower absorption rate and are taken only once a day.
The analysis used data on 3,198 women, aged 65 and older, observed annually between 1989-94. The data were part of a larger Cardiovascular Health Study, funded by the National Heart, Lung, and Blood Institute (NHLBI).
The analysis may raise concerns among those taking calcium channel blockers. The NHLBI, National Cancer Institute (NCI), and National Institute on Aging (NIA), all units of the National Institutes of Health, want to urge patients not to stop taking a calcium channel blocker without consulting their physician. Officials at these Institutes note that the dangers of uncontrolled high blood pressure may outweigh a possible cancer risk found in the study.
They also stress that these are preliminary findings and come from an observational study with a small number of cases. The findings do not establish a causal relationship between calcium blocker use and breast cancer.
Other observational analyses also have indicated a link between short-acting calcium channel blockers and cancer risk in older persons. Studies in the August 24, 1996 issue of The Lancet and the July 1996 issue of the American Journal of Hypertension found a significantly greater risk of cancer from short-acting calcium blockers than from beta blockers and ACE inhibitors, other high blood pressure medications.
Short-acting calcium channel blockers also have been linked with an increased risk of death from heart attack. This evidence led the NHLBI to warn physicians in September 1995 that one particular calcium channel blocker--short-acting nifedipine--should be prescribed "with great caution (if at all)" because of the increased risk of death from its use.
But more research is needed to confirm a relationship between calcium channel blockers and cancer. The NCI is funding research on calcium blockers and their possible association with breast cancer.
Findings from clinical trials are especially important. Ongoing, randomized, controlled clinical trials are being funded, including the NHLBI-sponsored ALLHAT (Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial). ALLHAT includes only a longer-acting calcium channel blocker. These trials are carefully monitored by independent experts to insure patient safety and drug efficacy.