MC1R and melanoma: Only sporadic and very old studies have dealt with the capacity of activated MC1R to modulate proliferation in melanoma cells and melanocytes: transformed cells respond to αMSH by proliferating or down-regulating proliferation, according to the degree of pigmentation and the progression of the pathology [13, 14]; primary cultures of human melanocytes respond to αMSH with a hyper-proliferative behaviour [1, 3, 15–17] and some authors have defined αMSH as a mitogenic agent for melanocytes [1, 3].