The investigational product, afamelanotide, is a synthetic analogue of the human alpha melanocyte stimulating hormone (alpha-MSH). The earliest described function of alpha-MSH is its ability to stimulate melanin synthesis in the skin and therefore stimulate pigmentation. Vitiligo is the most common depigmentation disorder. Interventions in the treatment of vitiligo include phototherapy with narrow-band (NB) ultraviolet B (UVB) irradiation (NB-UVB).