The HER2DX ERBB2 mRNA score was significantly associated with improved survival in patients with metastatic HER2+ BC. Breast cancer survivors with metabolic syndrome have shorter disease-free survival than those without metabolic syndrome. Breast cancer survivors have a modestly increased risk of type 2 diabetes, largely driven by breast cancer treatment. Using the HER2DX genomic tool is feasible in a real-world setting of patients with early-stage HER2-positive breast cancer. Patients with breast cancer who have high levels of glycosylated hemoglobin have an increased risk of recurrence and death. Breast cancer patients have an increased risk of cardiovascular disease compared with the general female population.