Among the compounds negatively related to the expression of HOX, 9 compounds belong to HDAC inhibitors, which are widely used as anti-tumor drugs (43), especially in the treatment of glioma, which means that inhibiting histone deacetylase may inhibit the expression of HOX, and the negative correlation between the compounds of this pathway and the expression of HOX can be found in 15 different cancers at most, including BLCA, CHOL, COAD, GBM, LUAD, and LUSC (Figure 6A). This evidence concerns the gene HDAC9 and central nervous system cancer.