Abstract
BACKGROUND: It is unclear whether diabetes and glycemic control affects the outcomes of breast cancer, especially among those with metastatic disease. This study aims to determine the impact of diabetes and hyperglycemia on cancer progression and mortality in individuals with metastatic breast cancer (MBC). METHODS: Patients with a diagnosis of MBC between 2010 and 2021 were identified using the MBC database at 2 academic institutions. We evaluated the effects of diabetes and glycemic control on overall survival (OS) and time to next treatment (TTNT). RESULTS: We compared 244 patients with diabetes (median age 57.6 years) to 244 patients without diabetes (matched for age, sex, ethnicity, and receptor subtype). OS at 5 years [diabetes: 54% (95% CI 47-62%) vs controls: 56% (95% CI 49-63%), P = 0.65] and TTNT at 1 year [diabetes: 43% (95% CI 36-50%) vs controls: 44% (95% CI 36-51%), P = 0.33] were similar between groups. A subgroup analysis comparing those with good glycemic control and those with poor glycemic control among patients with specific receptor subtype profiles showed no differences in OS at 5 years or TTNT at 1 year. In an 8-year landmark subgroup analysis, there was worse OS among individuals with diabetes compared to controls, and OS was found to be better among those with good glycemic control compared to those with poor control. CONCLUSIONS: Diabetes was not associated with increased mortality in individuals with MBC at 5 years. However, diabetes and hyperglycemia were associated with worse OS among a cohort of longer-term survivors. These findings suggest that individualized diabetes and glycemic goals should be considered in patients with MBC.