523Use of beta blockers and death from breast cancer in New Zealand breast cancer patients

Abstract

Abstract Background Beta blockers (BB), used for a range of cardiovascular indications, have been associated with improved, worsened, and unchanged breast cancer outcomes in previous studies. This study examines the association between the use of BBs and death from breast cancer in a large, representative sample of New Zealand women. Methods Women diagnosed with a first primary breast cancer between 2007 and 2016 were identified from four population-based regional NZ breast cancer registries and linked to pharmaceutical data, hospital discharges, and death records. The median follow up time was 4.51 years. Cox proportional hazard models were used to assess the hazard of breast cancer specific death (BCD) associated with post-diagnostic BB use. Results Of the 14,976 women included in analysis, 21% used a BB after diagnosis. Although not significant, beta blocker use increased the risk of BCD (adjusted hazard ratio: 1.08; 95% CI: 0.93-1.26). The increased risk was seen only in those with at least one cardiac condition, and was also reduced by lagging the exposure, suggesting effects of BB use close to the end of life. The increased risk was also confined to short term use (0-3 months). BB use for more than 1 year was associated with a decreased risk of BCD, and the risk steadily decreased to HR 0.53 (95% CI: 0.33-0.85) for use for 3+ years. Conclusions Any increased risk associated with BB use is likely to be due to a combination of confounding by indication and short-term use. Long-term BB use may confer some protection for BCD. Key messages The effect of beta blockers is difficult to separate from the indications for the drug. While there was no significant overall effect, there was a suggestion that beta blockers may be protective for breast cancer death with long-term exposure.