MMP9 and breast cancer: High concentrations of extracellular ATP have been also reported on breast cancer, where this situation was related to an increase in cancer invasion and metastatic potential, and overexpression of lysyl oxidase-like 2 (LOXL2) and matrix metalloproteinase-9 (MMP-9), which are direct targets of hypoxia-inducible factor 2α (HIF-2α), a relevant EMT agent [39].