MMP9 and breast cancer: LCN2 has been implicated in the progression of several types of human tumors, including breast cancer, through several mechanisms, such as stabilization of matrix metallopeptidase 9 (MMP‐9), sequestration of iron, induction of epithelial–mesenchymal transition, apoptosis resistance, lymphangiogenesis, and cell cycle arrest [16, 17, 18, 19, 20, 22, 23, 24, 25, 26].