Multivariate Cox proportional hazards regression analysis of the DFS of diabetic patients with hormone receptor-positive and HER2-positive breast cancer was carried out with a model consisting of the categorical covariates, age (<50 years versus ≥50 years), BMI (<25 kg/m2 versus ≥25 kg/m2), tumor size (T1 versus T2, 3, or 4), and node metastasis, using the metformin group as the reference. This evidence concerns the gene ERBB2 and breast cancer.