Along with the previous report that the enzymatic activity of urinary MMP-9/lipocalin-2 complex is detected in the urine of breast cancer patients but not in healthy control [11], several studies have suggested that circulating MMP-9, lipocalin-2 and MMP-9/lipocalin-2 complex could serve as a diagnostic and/or a prognostic biomarker in a variety of diseases with different suggested mechanisms [12-15]. Here, MMP9 is linked to breast cancer.