Pan-cancer analysis of the prognostic and immunological role of matrix metalloproteinase 9

Matrix metalloproteinase 9 (MMP9), a zinc ion-dependent endopeptidase, is one of the most complex matrix metalloproteinases in the gelatinase family. During tissue remodeling, MMP9 leads to gelatin and collagen degradation, which in turn promotes tumor invasion and metastasis. However, comprehensive pan-cancer analysis has not been performed for MMP9. In addition, the diagnostic and prognostic value of MMP9 as a cancer biomarker remain poorly understood, as well as the utility of MMP9 expression as a predictor of immunological responses. Based on a comprehensive analysis of bioinformatics information, we investigated MMP9 expression in different cancers, correlations between MMP9 expression and cancer prognosis and gene mutations, and relationships between MMP9 expression and immune cell infiltration. Our results indicated that MMP9 was highly expressed in most malignant cancers. MMP9 expression was significantly positively or negatively associated with the clinical prognoses of patients with different kinds of cancer. Furthermore, MMP9 expression significantly correlated with infiltrating cells and the expression levels of immune checkpoint genes. This pan-cancer analysis provides comprehensive information on the potential value of MMP9 as a theranostic biomarker.