Programmed cell death 1 (PD-1) inhibitor and programmed death ligand 1 (PD-L1) inhibitor are therapeutic agents that inhibit binding together of these checkpoint proteins on immune cells, eventually preventing tumors to escape the host immune defense mechanism and control the disease progression. Keytruda, a PD-1 inhibitor developed by Merck Sharp and Dhome (MSD) was the first to enter the...