The clustering analysis separated CTC marker genes into two major groups: (i) CD44, CXCR4, ICAM1, CCR1, and IL1R1 where high expression correlated with poor survival for low grade gliomas (LGG), kidney renal clear cell carcinoma (KIRC), for glioblastoma (GBM), kidney renal papillary cell carcinoma (KIRP) or lung squamous cell carcinoma (LUSC) (Figure 3C). This evidence concerns the gene CXCR4 and central nervous system cancer.