PDCD1 and prostate cancer: It is notable that findings of quantitative analysis of PD-1/PD-L1 imaging closely correlate with IHC analysis, which further provide a more comprehensive understanding of systemic immunity, for example, 89Zr-C4 PET in evaluating PD-L1 expression of NSCLC and prostate cancer (Truillet et al., 2018), 111In-PDL1.3.1 SPECT in evaluating PD-L1 expression of breast cancer (Heskamp et al., 2015), and 89Zr-nivolumab PET in evaluating PD-1 expression of advanced NSCLC (Niemeijer et al., 2018).