Risk of second breast cancer events with chronic opioid use in breast cancer survivors.

PURPOSE

Opioids may increase cancer risk and progression through multiple pathways. Our objective was to estimate the association between chronic opioid use and risk of second breast cancer events (SBCEs).

METHODS

Cohort study of women greater than or equal to 18 years, diagnosed with early stage breast cancer between January 1, 1990, and December 31, 2008, and enrolled in a large health plan for 1+ years before and after (unless died) diagnosis. SBCEs were defined as evidence of recurrence or second primary breast cancer in the medical chart. Chronic opioid use was defined as 75+ days of use in any moving 90-day window after breast cancer diagnosis and varied to 150+ days in a 180-day window in a sensitivity analysis. Using Cox proportional hazards models, we estimated hazard ratios (HRs) and 95% confidence intervals (CIs) for SBCE and components of SBCE by chronic opioid use.

RESULTS

Almost 10% met the criteria for chronic use and almost a third of users were taking opioids for greater than 3 years. Risk of SBCEs (HR = 1.20; 95% CI, 0.85-1.70), including second primary breast cancer (HR = 1.38; 95% CI, 0.71-2.70), was nonsignificantly higher among chronic users vs nonchronic/nonusers. The HR for recurrence was 1.14 (95% CI, 0.76-2.70). Results of the sensitivity analyses on longer opioid use does support an association with SBCE or recurrence.

CONCLUSION

This first US-based study on chronic opioid use and cancer outcomes provides some reassurance on safety. However, the question warrants further exploration in other populations and settings.