CD274 and lung cancer: CK−/PD-L1+ CTCs were detected in 66.7% (10/15) of PE with the quantity of 89.1 ± 95.8 cells/ml (Figure 4A), 50% (5/10) of CSF samples with the quantity of 14.1 ± 17.0 cells/mL (Figure 4B), and 32.3% (90/278) of blood samples with the quantity of 0.14 ± 0.44 cells/mL (Figure 4C), from advanced lung cancer patients, highlighting their widespread distribution across biofluids.