MMP9 and central nervous system cancer: Intriguingly, in the genes that are positively corelated with CE, these are a series of well‐documented genes that encode proteins promoting glioma cell malignancy, such as MMP9, an enzyme involved in the breakdown of the extracellular matrix; LIF, a cytokine that affects cell growth; and TWIST1, a transcription factor involved in epithelial‐mesenchymal transition.