PDCD1 and cancer: Based on this premise, Shen et al. [13] performed a meta-analysis to evaluate the efficacy of PD-1 or PD-L1 inhibitors in patients with cancer that were PD-L1 positive and PD-L1 negative; they concluded that PD-L1 expression could not sufficiently predict the therapeutic efficacy of PD-1/PD-L1 inhibitors.