Pembrolizumab (Keytruda(®)) is a humanized monoclonal antibody against programmed death receptor-1 (PD-1), a key immunoinhibitory checkpoint protein implicated in down-regulating anti-tumour immune responses. This intravenous drug is indicated for the treatment of advanced (unresectable or metastatic) melanoma, on the basis of its clinical benefit in this setting in the phase I KEYNOTE 001 trial (expansion cohorts) and the phase II and III trials, KEYNOTE 002 and 006.