Potential intrinsic subtype dependence on the association between metformin use and survival in surgically resected breast cancer: a Korean national population-based study.

Metformin administration may be associated with reduced mortality in patients with surgically resected breast cancer, particularly in the HT+/HER2 Tx- group. Clinical trials investigating metformin as a combination agent in breast cancer should stratify patients by curative resection, intrinsic subtype, the presence of T2DM, and the use of insulin.