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.