PD-L1, or Programmed Death-Ligand 1, is a protein that plays a critical role in suppressing the immune system by binding to the PD-1 receptor on T-cells, which can lead to immune evasion by cancer cells. The inhibition of the PD-1/PD-L1 pathway has become a pivotal strategy in cancer immunotherapy, leading to the development of checkpoint inhibitors that enhance the immune system's ability to target and destroy cancer cells.