ME3 and breast cancer: In mammalian cells, the family consists of three isoforms: a cytosolic NADP+‐dependent isoform (ME1), a mitochondrial NAD+‐dependent isoform (ME2), and a mitochondrial NADP+‐dependent isoform (ME3).[13] Among them, ME1 is the most abundant isoform, accounting for approximately two‐thirds of malic enzyme expression.[30] ME1 is frequently overexpressed in cancer cells, and knockdown of ME1 expression could induce ROS accumulation and suppress cell viability in either gastric or breast cancer.[31, 32]