SIGLEC15 and central nervous system cancer: Although no significant difference in Siglec15 expression was revealed between grade II and grade III in the TGGA datasets, Siglec15 expression levels were significantly higher in GBM (grade IV) than in low-grade gliomas (grade II and III) (TCGA: WHO grade II vs III, P = 0.224; WHO grade II vs IV, P <0.001; WHO grade III vs IV, P < 0.001; CGGA: WHO grade II vs III, P = 1; WHO grade II vs IV, P <0.001; WHO grade III vs IV, P < 0.001, Figure 1C).