As summarized in Table 2, genes expressed by the C6 glioma relevant to human GBMs include Cdkn2a, Cdkn2b, Pik3ca, and Cdkn2a and b with wild-type p53 mutations and mutant p16/Cdkn2a/Ink4a locus (26), with no expression of p16 and p19ARF mRNAs (27). This evidence concerns the gene PIK3CA and central nervous system cancer.