Classic ICIs include monoclonal antibodies targeting programmed cell death protein 1 (PD-1; pembrolizumab, nivolumab), programmed death ligand 1 (PD-L1, atezolizumab, durvalumab, avelumab), and CTLA-4 (ipilimumab).[156] In 2019, the US Food and Drug Administration (FDA) approved the first ICI treatment regimen for breast cancer (pembrolizumab). This evidence concerns the gene PDCD1 and breast cancer.