PDCD1 and neoplasm: This combined clinical study with a rapidly and slowly accumulating radiotracer (addressing PD-L1 and PD-1, respectively) revealed the heterogeneity of PD-L1 expression between and within tumor lesions, a positive correlation between tracer uptakes and PD-1/PD-L1 expression levels, and a relationship between the SUVpeak and the response rate for both tracers.