GSTP1 and glioblastoma: Interestingly, there are three known gene variants of GSTP1, and the gene variant (GSTP1*C) that we include in the Boolean function is the one, among the three, that was shown to contain functional retinoic acid response elements (RAREs) in its introns, confirmed by the observation that retinoic acid treatment significantly increased GSTP1*C gene expression in glioblastoma cells, a fact that may contribute to a better understanding of the molecular regulation of the GSTP1 gene in human cells [36] and provide possibilities for therapeutic intervention.