MMP9 and central nervous system cancer: Guan et al (2004) showed that PEDF-decreased invasion of malignant U251 glioma cells was related to downregulation of matrix-metalloproteinase-9 (MMP-9), an important enzyme for matrix degradation. Kozaki et al (1998) showed that PEDF secreted by colon cancer cells bound with high affinity to both collagen I and III and that expression of PEDF was inversely related to its metastatic capacity.