In glioblastoma cells, which express estrogen receptors and have the ability to synthesize estrogens, melatonin also reduces the local production of estrogens by decreasing the activity of aromatase, sulfatase and 17β-HSD1, and downregulating aromatase, sulfatase and 17β-HSD1 mRNA steady state levels (31,32). The gene discussed is CYP19A1; the disease is glioblastoma.