Type 2 diabetes, breast cancer specific and overall mortality: Associations by metformin use and modification by race, body mass, and estrogen receptor status

• Published in: PloS one 2020-05, Vol.15 (5), p.e0232581-e0232581
• Main Authors: Lee, Kyung Na, Torres, Mylin A, Troeschel, Alyssa N, He, Jiabei, Gogineni, Keerthi, McCullough, Lauren E
• Format: Article
• Language: English
• Subjects: Analysis; Antidiabetics; Biology and Life Sciences; Body mass; Breast cancer; Cancer research; College football; Confidence intervals; Diabetes; Diabetes mellitus; Diabetes mellitus (non-insulin dependent); Diabetes therapy; Diabetics; Diagnosis; Estrogens; Health aspects; Health hazards; Health risk assessment; Insulin resistance; Kinases; Medical diagnosis; Medicine and Health Sciences; Metformin; Mortality; Obesity; Patients; Phenols (Class of compounds); Statistical models; Type 2 diabetes; White women; Women; Women's health
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0232581

While type 2 diabetes (T2D) has been associated with increased all-cause mortality among women diagnosed with breast cancer (BC), the association between T2D and breast cancer-specific (BCS) mortality is unresolved. The goal of this study was to examine the association between T2D and BCS mortality and examine the influence of metformin treatment on mortality rates. A retrospective cohort study was conducted between 2002 and 2008 at Emory University Hospitals among non-Hispanic black and white women who had confirmed diagnosis of stage I-III BC and known diabetes status (T2D: n = 73; non-T2D: n = 514). Cox proportional hazard models were used to estimate hazard ratios (HR) and 95% confidence intervals (CI). Compared to non-T2D patients, T2D women had almost a 2-fold increase in BCS mortality after adjusting for covariates (HR = 2.01; 95%CI = 1.02-3.98). Though attenuated, the increased hazard of death was also observed for all-cause mortality (HR = 1.74; 95%CI = 1.06-2.87). T2D patients who were not on metformin had substantially higher hazard of BCS mortality compared to non-diabetic patients (HR = 4.54; 95%CI = 1.98-10.44), whereas the association among T2D patients treated with metformin was weak (HR = 1.20; 95%CI = 0.36-3.97) and included the null. Among women with BC, T2D is associated with increased BCS mortality. Metformin treatment for T2D during the initial diagnosis of BC may improve outcomes.