MGMT and glioblastoma: Key next steps should include: (1) quantify MGMT enzymatic activity and determine whether protein down-regulation translates into functional sensitization to temozolomide (TMZ) in vitro; (2) investigating the in vivo efficacy of ATRA, both alone and in combination with TMZ, using relevant orthotopic GBM models; and (3) extending these investigations to patient-derived GSC models to better assess translational potential.