ABCG2 and glioblastoma: In our study we found a significantly increased MGMT and ABCB1 promoter methylation in GBM tissue but couldn’t demonstrate any association of MGMT, ABCB1 or ABCG2 promoter methylation with overall survival of glioblastoma patients in multivariate Cox models adjusted for potential risk factors (gender and age) and stratified on the variable therapy (temozolomide vs. no temozolomide).