Beta blockers and breast cancer mortality: A population-based study

Purpose: Preclinical studies have demonstrated that antagonism of β₂-adrenergic signaling inhibits several pathways necessary for breast tumor progression and metastasis. A series of population-based observational studies were conducted to examine associations between beta blocker use and breast tumor characteristics at diagnosis or breast cancer-specific mortality. Patients and Methods: Linked national cancer registry and prescription dispensing data were used to identify women with a diagnosis of stage I to IV invasive breast cancer between January 1, 2001, and December 31, 2006. Women taking propranolol (β₁/β₂ antagonist; n = 70) or atenolol (β₁ antagonist; n = 525), in the year before breast cancer diagnosis were matched (1:2) to women not taking a beta blocker (n = 4,738). Associations between use of propranolol or atenolol and risk of local tumor invasion at diagnosis (T4 tumor), nodal or metastatic involvement at diagnosis (N2/N3/M1 tumor), and time to breast cancer-specific mortality were assessed. Results: Propranolol users were significantly less likely to present with a T4 (odds ratio [OR], 0.24, 95% CI, 0.07 to 0.85) or N2/N3/M1 (OR, 0.20; 95% CI, 0.04 to 0.88) tumor compared with matched nonusers. The cumulative probability of breast cancer-specific mortality was significantly lower for propranolol users compared with matched nonusers (hazard ratio, 0.19; 95% CI, 0.06 to 0.60). There was no difference in T4 or N2/N3/M1 tumor incidence or breast cancer-specific mortality between atenolol users and matched nonusers. Conclusion: The results provide evidence in humans to support preclinical observations suggesting that inhibiting the β₂- adrenergic signaling pathway can reduce breast cancer progression and mortality.