MMP9 and breast cancer: Within the protein family of proteases degrading the extracellular matrix, both gelatinases A and B—metalloproteinases MMP-2 and MMP-9, respectively—are well known prognostic factors that, when elevated, are indicators of poor outcomes for oncologic patients in general, and, in particular, promoting liver metastases [11, 12], metastatic disease in the most aggressive breast cancer phenotypes (such as triple-negative breast cancer) [13] and formation specifically of liver metastases in breast cancer [14].