Use of beta‐blockers and risk of contralateral breast cancer.

Beta‐blockers have shown antineoplastic effects in laboratory studies but epidemiologic evidence in relation to contralateral breast cancer (CBC) is sparse. We investigated postdiagnosis beta‐blocker use and risk of CBC in a cohort of 52 723 women with breast cancer by using nationwide Danish health registers and the Danish Breast Cancer Group database. We defined postdiagnosis beta‐blocker use as a time‐varying covariate starting 1 year after a second prescription was redeemed. Cox proportional hazards regression was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for CBC associated with beta‐blocker use compared to nonuse. We identified 1444 women with CBC of whom 209 women were beta‐blocker users. We found an overall HR of 1.08 (95% CI: 0.93‐1.27) for beta‐blocker use and risk of CBC with no substantial variation according to cumulative amount, intensity or selectivity of beta‐blocker use. Hence, our cohort study of women with breast cancer did not sustain a protective effect of beta‐blocker use on risk of CBC, irrespective of beta‐blocker type. [ABSTRACT FROM AUTHOR]