CD274 and non-small cell lung carcinoma: The profile of Exo-PD-L1 was determined by ELISA and the results showed that Exo-PD-L1 levels of I-II (15.90 ± 6.45 pg/ml serum) and III/IV NSCLC patients (21.10 ± 11.63 pg/ml serum) were considerably higher than that of healthy controls (15.91 ± 6.45 pg/ml serum) (p < 0.05 and p < 0.001, respectively) (Fig. 3a).