MMP9 and breast cancer: Tumor-associated neutrophils by secreting the cytokine tissue inhibitor matrix metalloproteinase 1 (TIMP-1) induce breast cancer EMT and can also remodel the extracellular matrix via neutrophil collagenase (MMP8) and gelatinase B (MMP9) (Giese et al., 2019; Wang et al., 2019).