XAF1 and glioblastoma: Furthermore, genes linked with cancer cell survival having proapoptotic functions were inactivated by hypermethylation, as in the case of XAF1 (XIAP-associated factor 1) gene that is frequently hypermethylated in human urogenital cancers and contributes to the malignant progression of tumors [18], or CASP8 (caspase 8) gene that was reported to be hypermethylated after glioblastoma multiforme relapse [19].