Pan-Cancer Bioinformatics Analysis of Matrix Metalloproteinase-9 (MMP9).

Background: Matrix metalloproteinase-9 (MMP9) is a member of the matrix metalloproteinase family of proteases that have been linked to several major normal and pathologic processes. Although cell-based, animal-based, or clinical-based evidence supports the relationship between MMP9 and cancers, the role of MMP9 in pan-cancer is still not fully understood.

Methods: We explored the prognostic value and potential immunological roles of MMP9 in 33 cancer types using the Cancer Genome Atlas datasets.

Results: MMP9 is highly expressed at the RNA level in most cancers but is present at a low protein level in breast cancer, liver cancer, lung adenocarcinoma, and ovarian cancer. Furthermore, there are distinct associations be-tween MMP9 expression and tumor patient prognosis. MMP9 expression was found to be associated with tumor mutational burden and microsatellite instability in eight cancer types, whereas it was associated with DNA methylation at multiple probes in 31 cancer types. Additionally, MMP9 expression was positively associated with the infiltration levels of most immune cells in 33 cancer types. Moreover, extracellular matrix organizing-related and collagen metabolism-related functions are involved in the functional mechanism of MMP9.

Conclusions: Our pancancer study offers a relatively comprehensive understanding of the role of MMP9 in tumorigenesis and tumor immunity in different tumors.