In a final study by Natarajan et al., the 64Cu human PD-1 tracer was evaluated in NSG mice xenografted with 293 T/hPD-1 stable non-cancer cells and in NSG mice with adoptively transferred hPMBCs xenografted with A375 human melanoma cells (Natarajan et al. 2018a). This evidence concerns the gene PDCD1 and cancer.