MMP9 and gastric cancer: Matrix metalloproteinases (MMPs) are members of a family of at least 23 Zn2+-dependent proteases that are involved in the degradation and remodeling of the extracellular matrix and basement membrane, as well as other growth factors, cytokines, and chemokines, during normal and pathologic biological processes.1 MMP9 is an extracellular enzyme involved in matrix remodeling during tumor growth and metastasis, and it is a poor prognostic factor for gastric cancer.