PDCD1 and breast cancer: Subsequently, pembrolizumab and nivolumab, antibodies that block programmed cell death protein-1 (PD-1), were effectively used to treat a variety of tumors, such as renal cell carcinoma (RCC) [10], advanced melanoma [10, 11], non-small-cell lung cancer (NSCLC) [10], breast cancer [5, 12], and advanced hepatocellular carcinoma [13].