Similar to our own data, no differences were detected in the promoter and gene DNA CpG methylation levels when the primary and recurrent GBM pairs were compared (ADRA1D: 8.33 (16.66–3.84) and 8.01 (19.38–3.84); ADRBK1:17.46 (28.85–8.35) and 18.98 (33.40–9.87); DRD2: 4.59 (7.95–2.14) and 5.96 (9.17–2.75); SCL18A2: 5.96 (11.37–3.25) and 7.58 (13.00–3.25)) (Figure 4). This evidence concerns the gene GRK2 and glioblastoma.