Evaluation of clinicopathological factors in PD-1 response: derivation and validation of a prediction scale for response to PD-1 monotherapy
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. These studies were conducted in ipilimumab-naïve and/or ipilimumab-experienced patients and assessed varying pembrolizumab regimens administered every 2 or 3 weeks, all of which helped to determine the recommended dosage of 2 mg/kg every 3 weeks. In the trials with active comparator arms, pembrolizumab regimens significantly improved progression-free survival (PFS), overall survival (OS) and overall response rates (ORR) relative to ipilimumab in ipilimumab-naïve patients (KEYNOTE 006), and significantly improved PFS and ORR, but not OS (although OS data are immature), relative to chemotherapy in ipilimumab-refractory patients, who had also received BRAF/MEK inhibitor therapy if BRAF-mutation positive (KEYNOTE 002). Pembrolizumab has an acceptable tolerability profile, with immune-related adverse events that are generally manageable/reversible. Thus, pembrolizumab is a valuable treatment option for patients with advanced melanoma, including those who have progressed on ipilimumab and BRAF/MEK inhibitors.