MT3 and cancer: Furthermore, it is known that the activation of melatonin is mediated by G protein-coupled receptor melatonin receptor type 1, 2, and 3 (MT1, MT2, MT3, respectively, and directly) or the retinoid-related orphan nuclear receptor α (RZR/RORα, indirectly), and these receptors serve as attractive targets for a series of biological processes such as immunomodulation, endocrine regulation, and cancer formation (Foldes et al., 1992; Slominski et al., 2012).