Along with MGMT gene methylation, retinoic acid receptor β (RARβ) promoter methylation is also positively correlated with treatment responses to radiotherapy and chemotherapy in GBM, suggesting RARβ-targeting therapies as potential candidates (including the FDA-approved drugs sulfanilamide, fulvestrant, sulfamerazine, bacampicillin, myricetin, and fursultiamine) [64]. Here, RARB is linked to glioblastoma.