Associations between antidiabetic medication use and breast cancer survival outcomes among medicare beneficiaries

Objective: This study examined the associations between mortality (all-cause and breast cancer-specific) and different antidiabetic medication use before breast cancer diagnosis. Methods: This study used a longitudinal, retrospective cohort design. Linked Surveillance, Epidemiology and End Results (SEER)-Medicare databases from 2007 to 2013 were used to identify female beneficiaries who had continuous Medicare enrollment, a new breast cancer diagnosis between 2008 and 2013, and exposure to the antidiabetic medication. Different classes of antidiabetic medications from one year before their breast cancer diagnosis were considered as users while all other non-users were excluded. Both all-cause mortality and breast cancer-specific mortality were treated as outcomes. Cox proportional hazards models for all-cause mortality and sub-distribution hazards models for breast cancer-specific mortality were employed to estimate both unadjusted and adjusted hazard ratios and 95% confidence intervals (CI) for risks of survival outcomes, controlling for severity of diabetes and other covariates. Key findings: A total of 1715 women with breast cancer used antidiabetic medications one year before their breast cancer diagnosis. Compared to metformin, women using insulin, sulfonylurea and combination treatments before their breast cancer diagnosis had a higher risk for all-cause mortality (adjusted Hazard Ratio, aHR: 1.64, 95% CI 1.29, 2.07; aHR: 1.35, 95% CI 1.04, 1.75 and aHR: 1.44, 95% CI 1.14, 1.83, respectively). Women with advanced-stage breast cancer and higher levels of diabetes severity were more likely to get all-cause mortality (all P < 0.05). Women with combination treatments had a statistically higher risk of breast cancer-specific mortality (aHR: 1.52, 95% CI 1.05, 2.19) than metformin users. Conclusions: Among women with breast cancer, mortality risk is associated with pre-diagnosis exposure to different types of antidiabetic medications.