Drug use disorder and risk of incident and fatal breast cancer : a nationwide epidemiological study

Purpose: Breast cancer is one of the most common cancer forms in women and it is often detected by screening. However, women with drug use disorders (DUD) are less likely to be reached by screening programs. In this study, we aimed to investigate breast cancer incidence, mortality and stage at time of diagnosis among women with DUD compared to the general female population in Sweden. Methods: We performed a follow-up study based on Swedish national register data for the period January 1997–December 2015. The study was based on 3,838,248 women aged 15–75 years, of whom 50,858 were registered with DUD. Adjusted hazard ratios (HRs) for incident and fatal breast cancer, and cancer stage at time of diagnosis, were calculated for women with and without DUD using Cox regression analysis. Results: DUD was associated with incident breast cancer (HR 1.08, 95% confidence interval [CI] 1.02–1.14, p = 0.0069), fatal breast cancer (HR 1.60, 95% CI 1.42–1.82, p < 0.001), and stage IV breast cancer, i.e. metastasis at diagnosis (HR 2.06, 95% CI 1.44–2.95, p < 0.001). Conclusions: Women with DUD were identified as a risk group for incident, fatal and metastasized breast cancer, which calls for attention from clinicians and policy makers. Cancer screening attendance and other healthcare seeking barriers are likely to affect the risk increase among women who use drugs; however, more research is needed on the underlying mechanisms.