PDCD1 and neoplasm: Ten of the top 100 references with the strongest citation bursts in documents about the PD1/PDL1 molecule followed the rules and mainly focus on the molecular mechanism of action of PD1/PDL1 on T cells in the tumor microenvironment (Supplementary Material S4) (Carter et al., 2002; Dong et al., 2002; Blank et al., 2004).