We therefore took advantage of a large BC patient dataset with long follow-up (8 years or longer) to retrospectively analyze the effect of metformin treatment on the clinical outcome in a cohort of 4648 female patients with early, hormone receptor-positive/HER2-negative BC, who underwent surgery followed by anti-hormonal treatment (thus, tumors with the same setting and molecular characteristics as used in our scRNA-seq cohort) (Fig. 6a; Supplementary Data 1). The gene discussed is ERBB2; the disease is breast cancer.