Prior preclinical studies of metformin’s effects on FAO have focussed on mouse embryonic fibroblasts (MEFs), hepatocytes, hepatoma and cardiac and skeletal muscle cell models demonstrating increased FAO in an AMPK-dependent manner with a resultant decrease in cellular lipid content.16–20 However, in our cell line models of breast cancer, metformin inhibited FAO. This evidence concerns the gene PRKAA1 and breast cancer.