However, several studies (Jesien-Lewandowicz et al. (2009) on 32 primary GBMs from Polish patients [35]; Kalkan et al. (2015) on 40 primary GBMs from Turkish patients [36]; Ilić et al. (2017) on 62 GBMs from Serbian patients [37]; and Egaña et al. (2020) on 107 high-grade gliomas from Spanish patients) [38], including our previous study (Jovanović et al. (2019) on 25 GBMs from Serbian patients) [22], did not confirm the prognostic and/or predictive value of MGMT promoter methylation. This evidence concerns the gene MGMT and central nervous system cancer.