INS and diabetes mellitus: A recent retrospective cohort study of 3553 patients with breast cancer and DM showed significant survival differences among the non-diabetes group, metformin group, and insulin group; the five-year disease-free survival rate (DFS) was 85.8%, 96.1%, and 73.0%, and the five-year overall survival (OS) was 87.3%, 97.1%, and 73.3%, respectively.