Beta blocker use and breast cancer survival by subtypes: A population-based cohort study.

BACKGROUND: The associations between beta blocker (BB) use and breast cancer outcomes have been examined in previous observational studies, however the results are inconsistent. We examine these associations in a large population-based cohort of New Zealand (NZ) women with breast cancer. METHODS: Postmenopausal women diagnosed with a first primary early invasive breast cancer between 2006 and 2020 were identified from the NZ Breast Cancer Foundation National Register and linked to national pharmaceutical data, hospital discharges, and death records. Cox proportional hazard models were used to estimate hazards of breast cancer-specific death (BCD), recurrence free interval (RFI), and distant recurrence free interval (DRFI) associated with BB use at diagnosis. Analyses were stratified by subtype. RESULTS: Of the 13,535 women included in analyses, 2,238 (17 %) were using a BB at diagnosis and the median follow up time with BCD as the outcome was 5.6 years. BB use (vs non-use) was not associated with BCD (adjusted hazard ratio: 1.03; 0.86-1.23), RFI (HR = 0.94; 0.81-1.09), or DRFI (HR = 0.98; 0.83-1.15) overall. In women with triple negative breast cancer (TNBC), BB use was associated with a significantly longer RFI (HR = 0.71; 0.52-0.98) and DRFI (HR = 0.70; 0.50-0.98), and there was a suggestion of a decreased risk of BCD (HR = 0.74; 0.52-1.06). BB use was also associated with a significantly longer RFI in women with Luminal B HER2+ cancers (HR = 0.52; 0.29-0.92). CONCLUSIONS: Our findings suggest that any protective effect on breast cancer prognosis associated with BB use may be confined to specific subtypes, particularly TNBC.