New-Onset Diabetes after an Obesity-Related Cancer Diagnosis and Survival Outcomes in the Women’s Health Initiative

Background: Individuals diagnosed with an obesity-related cancer (ORC survivors) are at an elevated risk of incident diabetes compared with cancer-free individuals, but whether this confers survival disadvantage is unknown. Methods: We assessed the rate of incident diabetes in ORC survivors and evaluated the association of incident diabetes with all-cause and cancer-specific mortality among females with ORC in the Women’s Health Initiative cohort (N = 14,651). Cox proportional hazards regression models stratified by exposure-risk periods (0–1, >1–3, >3–5, >5–7, and >7–10 years) from ORC diagnosis and time-varying exposure (diabetes) analyses were performed. Results: Among the ORC survivors, a total of 1.3% developed diabetes within ≤1 year of follow-up and 2.5%, 2.3%, 2.3%, and 3.6% at 1–3, 3–5, 5–7, and 7–10 years of follow-up, respectively, after an ORC diagnosis. The median survival for those diagnosed with diabetes within 1-year of cancer diagnosis and those with no diabetes diagnosis in that time frame was 8.8 [95% confidence interval (CI), 7.0–14.5) years and 16.6 (95% CI, 16.1–17.0) years, respectively. New-onset compared with no diabetes as a time-varying exposure was associated with higher risk of all-cause (HR, 1.27; 95% CI, 1.16–1.40) and cancer-specific (HR, 1.17; 95% CI, 0.99–1.38) mortality. When stratified by exposure-risk periods, incident diabetes in ≤1 year of follow-up was associated with higher all-cause (HR, 1.76; 95% CI, 1.40–2.20) and cancer-specific (HR_0–1, 1.82; 95% CI, 1.28–2.57) mortality, compared with no diabetes diagnosis. Conclusions: Incident diabetes was associated with worse cancer-specific and all-cause survival, particularly in the year after cancer diagnosis. Impact: These findings draw attention to the importance of diabetes prevention efforts among cancer survivors to improve survival outcomes.