Abstract B134: Type 2 diabetes and breast cancer recurrence in the population-based Carolina Breast Cancer Study

Abstract Background: Prior studies report mixed findings on the link between type 2 diabetes (T2D) and breast cancer (BC) recurrence, with some suggesting increased risk and others showing no association. While T2D may promote BC growth, it may also reflect and result in more healthcare system engagement. Therefore, T2D may have pleiotropic effects on BC recurrence. However, many of these studies have been limited by sample sizes and low T2D prevalence, and therefore inability to stratify by estrogen receptor (ER) status. In our study conducted in the southeastern United States, the prevalence of T2D was 15%, allowing for ER-stratified analyses. Objective: To evaluate the association between T2D and BC recurrence, overall and stratified by ER status. Methods: This analysis considered individual-level demographic and clinical data (age at diagnosis, race, body mass index, tumor stage at diagnosis, clinical tumor subtype, and ER status) from the Carolina BC Study Phase 3, a population-based cohort of women diagnosed with invasive BC from 2008-13 (n=2,998). T2D, age, tumor stage, and ER status were abstracted from medical records. Clinical subtype was abstracted from pathology reports. Recurrence among participants with T2D (n=430) was compared to that among those without T2D (n=2,459) using Cox proportional hazards models. Hazard ratios (HR) and 95% confidence intervals (CIs) were estimated for the relationship between BC recurrence and T2D at 5 and 10 years, adjusting for age (<50 vs ≥50 years), race (Black vs non-Black), and stage (3 vs 2 vs 1). Additional models adjusted for BMI (obese vs non-obese) alone or BMI and clinical subtype (HER2+ vs HR-/HER2- vs HR+/HER2-). Analyses were stratified by ER status. Results: Adjusting for age, race, stage, BMI, and clinical subtype, T2D was not statistically significantly associated with 5- or 10-year BC recurrence: aHRs were 1.10 (95% CI: 0.84-1.46) for 5 years and 1.14 (95% CI: 0.86-1.50) for 10 years. In ER-stratified models, aHRs for women with ER-positive tumors were positive but not statistically significant: aHRs were 1.18 (0.81-1.71) for 5 years and 1.24 (0.85-1.08) for 10 years. Among women with ER-negative tumors, associations were null: aHRs were 1.01 (95% CI: 0.66-1.53) and 1.01 (95% CI: 0.67-1.54). Conclusion: T2D was not significantly associated with 5- or 10-year BC recurrence overall or by ER status. These null findings are consistent with prior studies. Engagement with the healthcare system may mitigate some of the biological effects of T2D, however future work should contextualize these findings amid other common comorbidities among breast cancer patients. Citation Format: Joel A. Begay, Qichen Wang, Marc A. Emerson, Melissa A. Troester. Type 2 diabetes and breast cancer recurrence in the population-based Carolina Breast Cancer Study [abstract]. In: Proceedings of the 18th AACR Conference on the Science of Cancer Health Disparities; 2025 Sep 18-21; Baltimore, MD. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2025;34(9 Suppl):Abstract nr B134.