This requires investigation in GBM/GSC, including whether TrkB induction is co-ordinated with an increase in YY1, and the “backward” conversion of melatonin to NAS by CYP1B1, mGluR5, P2Y1 receptor, CYP2C19 and/or O-demethylation. The gene discussed is CYP2C19; the disease is glioblastoma.