PDCD1 and breast cancer: An antibody against PD-1, either expending the epitope areas of nivolumab and pembrolizumab, particularly the “hotspot”- FG loop1, or recognizing N-glycan, especially the N58-glycan in the BC loop will likely to facilitate a more comprehensive understanding of PD-1 and therapeutic antibody binding, and show differentiation to commercially available PD-1 antibodies.