PDCD1 and neoplasm: In turn, the circFGFR1, which is significantly overexpressed in NSCLC tissues, acts as a tumor promoter by upregulating the C-X-C motif chemokine receptor 4 (CXCR4), a target gene for miR381-3p, and contributing to anti-PD-1 (Programmed cell Death Protein 1) resistance by sponging miR-381-3p (Zhang et al., 2019).