PDCD1 and neoplasm: In-vivo pharmacokinetics and whole-body distribution of [89Zr]labeled PD-1 targeting pembrolizumab with PET in humanized mice have been recently studied by van der Veen et al. [83], with disappointing results: tumor uptake of [89Zr]pembrolizumab was lower than uptake in normal lymphoid tissue, but higher compared to other organs.