Background: The use of calcium channel blockers in an elderly population recently was reported to be associated with the incidence of cancer. The Cardiovascular Health Study, a multisite observational cohort study, provided the opportunity to investigate the epidemiologic association between the use of calcium channel blockers and breast carcinoma risk in 3198 women age > or = 65 years.
Methods: Standard questionnaires and clinical procedures were administered at four study sites annually from 1989-1990 to 1993-1994. Drug usage was assessed by a medication inventory and hospitalizations for 75 incident invasive breast carcinoma cases were identified using International Classification of Diseases-9 Clinical Modification codes. Time-dependent Cox proportional hazards regression models were used to assess associations between incident breast carcinoma and the use of specific antihypertensive medication including calcium channel blockers.
Results: In adjusted Cox proportional hazards models, an elevated risk of breast carcinoma was associated with use of calcium channel blockers (hazard ratio [HR]: 2.57; 95% confidence interval [CI], 1.47-4.49). This association persisted when the comparison group was users of other antihypertensive medication. No associations between the use of other antihypertensive medication with incident breast carcinoma were found. Associations were enhanced by assessment of high dose at baseline (HR: 4.42; 95% CI, 1.37-14.27) and when calcium channel blockers were combined with estrogen use (HR: 4.48; 95% CI, 1.58-12.75). The association was found to be strongest for the use of estrogens with immediate release calcium channel blockers (HR: 8.48; 95% CI, 2.99-24.08).
Conclusions: Although the number of cases was limited in this observational study, associations found between the use of calcium channel blockers and incident invasive breast carcinoma warrant further investigation. Site specific carcinomas should be included as an outcome of ongoing and planned long term clinical trials using calcium channel blockers.