Risk of Newly Incident Diabetes Mellitus and Treatment Risk Factors in Breast Cancer Survivors: Landmark Analyses of Nationwide Data.

This study investigated temporal patterns and risk factors for diabetes mellitus (DM) in breast cancer survivors, stratified by age. Using a Korean database, this nationwide cohort study analyzed 65 982 breast cancer survivors and 168 214 matched controls. We assessed DM risk using multivariable Fine-Gray models with landmark analyses, stratifying by age (≤50 and >50 years). Diabetes mellitus risk peaked in the first year post-diagnosis for women ≤50 (sub-distribution hazard ratio [sHR] = 3.74; 95% confidence interval CI [3.08, 4.55] and >50 (sHR = 1.71; 95% CI [1.52, 1.93], with risk diminishing thereafter. Significant risk factors included high body mass index, smoking, hypertension, dyslipidemia, and taxane use. Tamoxifen was a specific risk factor for younger women (sHR = 1.22; 95% CI [1.06, 1.40]). Breast cancer survivors, especially younger women, have the highest DM risk within the first year post-diagnosis. Proactive monitoring is crucial for those with established clinical and treatment-related risk factors.