In October 2016, pembrolizumab became the new standard of care for firstline treatment of patients with metastatic non–small cell lung cancer (mNSCLC) whose tumors express programmed death ligand 1 in at least 50% of cells. The US Food and Drug Administration–recommended dose is 200 mg every three weeks. Multiple studies have demonstrated equivalent efficacy with weight-based doses between 2 mg/kg and 10 mg/kg. The objective of this study was to compare the economic impact of using personalized dosing (2 mg/kg) vs fixed dosing (200 mg) in the firstline setting of mNSCLC.