1422-P: The Impact of Type 2 Diabetes Mellitus on the Clinical Outcome of Breast Cancer

Objectives: Women with breast cancer and diabetes have worse outcomes than those with breast cancer without diabetes. The objective of this study was to investigate the impact of pre-existing diabetes on breast cancer prognosis. Methods and Materials: This was a retrospective observational study using Cancer database from a single tertiary center. The study population included women aged ≥20 years with breast cancer diagnosed between 1 January 2014 and 31 December 2018. Patients were categorized by diabetes status (T2D: n=111, non-T2D: n= 889). The clinicopathological features and outcomes were collected and compared between women with and without diabetes. Cox proportional hazard regression was used to estimate adjusted hazard ratios for overall mortality. Results: Compared to non-T2D patients, T2D patients were significantly older, had higher BMI, were more post-menopausal state at breast cancer diagnosis, had more comorbid conditions, and were in lower educational states. There were no statistically significant differences in tumor characteristics, including metastasis, lymph nodes, grade, and extent of surgery. Women with T2D had a significantly increased risk of overall mortality after adjusting for demographic and traditional risk factors for breast cancer (HR=2.15; 95%CI=1.10-4.20). Compared to patients with pre-existing T2D (n=111), patients with newly diagnosed T2D after receiving a breast cancer diagnosis (n=34) had a lower risk of breast cancer recurrence (HR=0.30; 95%CI=0.10-0.94). Conclusion: Our study showed that pre-existing T2D and T2D itself increase the risk of recurrence and total mortality among patients with breast cancer. These findings provide important prognostic information for the treatment of women with both T2D and breast cancer. Therefore, diabetes deserves additional attention to assess possible causal relationships that potentially could be modified to improve outcomes.