NTRK2 and neoplasm: Such emphasis on the under-investigated tryptophan-melatonin pathway in tumor microenvironment cells is supported by data indicating the importance of the mitochondrial melatonergic pathway to the long-standing and continuing evolution of multicellular life on Earth [25], as well as the presence of mitochondrial receptors intimately associated with the mitochondrial melatonergic pathway, such as the AhR, TrkB and α7nAChR.