BDNF and cancer: The O-demethylation of melatonin to NAS is of some importance in the tumor microenvironment as tumor cell exposure to melatonin invariably leads to tumor apoptosis [29], whilst NAS exposure may enhance the survival and proliferations of cancer stem-like cells via the capacity of NAS to mimic brain-derived neurotrophic factor (BDNF) by activating the BDNF receptor, tyrosine receptor kinase B (TrkB) [30].