Drugs intended to treat cardiovascular conditions such as high blood pressure (hypertension) and heart failure appear to have varying influences on breast cancer risk and metastasis. For example, several studies have reported that use of beta blockers appears to reduce metastasis and mortality in breast cancer patients. In fact, the beta blocker propranolol (Inderal) has been shown to strengthen the anti-tumor efficacy of Taxol (paclitaxel) and 5-FU (5-fluorouracil) chemotherapy. Results have been less consistent for ACE inhibitors (angiotensin-converting enzyme inhibitors) and calcium channel blockers, with some studies reporting associations between use of these drugs and increased breast cancer risk. Now a new study has reported that long-term use of calcium channel blockers is associated with increased risk of breast cancer, especially among overweight and obese women.

Calcium channel blockers and breast cancer

As outlined below, most studies have reported that use of calcium channel blockers is not associated with breast cancer risk. However, when the data is analyzed according to breast cancer type, type of calcium channel blocker or duration of use, some associations between calcium channel blockers and increased breast cancer risk have been reported.

  • A 2016 U.S. prospective study of 15,817 women between the ages of 35 and 74 at baseline found no evidence of increased risk of breast cancer from taking calcium channel blockers for 10 years or more.
  • A 2016 U.K. study of 273,152 women treated with antihypertensive drugs reported that use of calcium channel blockers was not linked to increased risk of breast cancer overall compared to use of other blood pressure drugs. Long duration of use did not alter this result.
  • Another 2016 study of 794,533 Taiwanese women reported increased risk of breast cancer among those who took dihydropyridine calcium channel blockers (i.e., amlodipine, felodipine and other calcium channel blockers with names ending in "dipine"). However, this result was not statistically significant.
  • A 2015 study of 210,641 participants in the Nurses Health Study (NHS) and Nurses Health Study II (NHS II) reported that antihypertensive medication use, including calcium channel blocker use, was largely unrelated to breast cancer risk.
  • Another 2015 study found no link between use of antihypertensive medications, including calcium channel blockers, and the risk of second primary contralateral breast cancer (i.e., recurrence in the other breast).
  • A 2014 meta-analysis of data from 17 previous studies concluded that long-term use of calcium channel blockers was associated with increased breast cancer risk. Use of nifedipine (Procardia, Adalat) was associated with significantly increased breast cancer risk whereas use of diltiazem (Cardizem, Dilacor) was not.
  • A 2013 meta-analysis of data from 11 previous studies concluded that use of immediate-release calcium channel blockers was associated with increased breast cancer risk whereas use of sustained-release was not.
  • A 2013 study of women aged 55 to 74 years in Washington state reported that use of calcium-channel blockers for 10 years or longer was associated with more than double the risk of ductal breast cancer (2.4 times) and lobular breast cancer (2.6 times) than non-use.
The fact that recent studies did not find an association between use of calcium channel blockers (including long-term use) and increased breast cancer risk appeared to put the matter to rest. However, as the study described below shows, the association may differ according body mass index (BMI) and type of breast cancer.

Latest research finds long-term use of calcium channel blockers increases risk

The Spanish case-control study referenced at the beginning of this news story was designed to investigate the associations between use of antihypertensive drugs and risk of breast cancer. The study included 1,736 breast cancer cases and 1,895 healthy controls. Results were analyzed according to menopausal status, BMI, breast cancer type, and duration of antihypertensive drug use.

Women using calcium channel blockers for at least five years were found to have 1.77 times the risk of breast cancer compared to non-users. The risk associated with calcium channel blockers was higher in women who were overweight or obese (BMI ≥ 25), who had 2.54 times the risk. Calcium channel blocker use was more strongly associated with more non-ductal (primarily lobular) (3.97 times the risk for non-users) and HER2+ (2.97 times) breast cancer. In addition, use of angiotensin II receptor blockers was found to be associated with increased risk of breast cancer among premenopausal women; this result did not differ by type of breast cancer. Use of beta blockers, ACE inhibitors, and diuretics were not found to be associated with breast cancer risk. The authors conclude that, according to this large population-based study, long-term use of calcium channel blockers is associated with increased risk of breast cancer in overweight women and with some subtypes of breast cancer.