Impact of Breast Cancer on Cardiometabolic Health in Spanish Women ≥50 Years with Pre-Existing Type 2 Diabetes Mellitus

During breast cancer (BC), cardiometabolic disorders can worsen prognosis, particularly in women with type 2 diabetes mellitus (T2DM). This study aimed to determine the impact of BC diagnosis on cardiometabolic parameters and the incidence of complication in women over 50 years of age (90% aged ≥ 65 years) with pre-existing T2DM. Using primary care registries from Asturias (Spain), a total of 106 women diagnosed with T2DM followed by BC were selected and matched with women with T2DM (<i>n</i> = 212) in a cohort study. Indicators of cardiometabolic health and microvascular complications associated with T2DM were collected. Women were monitored from two years prior to five years after BC diagnosis. Conditional logistic regressions were used to compare the adjusted odds of staying below each indicator's threshold. During follow-up, women with T2DM+BC had a higher risk of fasting blood glucose ≥126 mg/dL (adjusted odds ratio [aOR] = 1.83; 95% confidence interval [CI95%]: 1.01-3.32) and glycosylated hemoglobin (Hb1Ac) ≥ 48 mmol/mol or 6.5% (aOR: 2.44; IC95%: 1.21-4.91). There was no difference between the groups regarding the incidence of microvascular complications. BC incidence negatively impacted the glycemic control of Spanish women with pre-existing T2DM measured by basal blood glucose and HbA1c, but not cardiometabolic health indicators or T2DM complications.