Advances in Small Molecule Drugs Targeting PD-1/PD-L1 PD-1/L1 antibodies can be said to be the current hot direction in the development of targeted cancer drugs. However, monoclonal antibodies have many inherent drawbacks, including poor oral bioavailability, prolonged tissue retention time and half-life, poor membrane permeability, transportation and storage, etc. In addition, the high cost of antibody drugs is also a non-negligible problem. Therefore, more and more researchers are exploring small molecule drugs as PD-1/L1 inhibitors to circumvent the disadvantages of therapeutic antibodies.