Conclusions
PD-L1 protein expression was significantly higher in smoking-associated adenocarcinoma and in EGFR mutation-negative adenocarcinoma. PD-L1 protein expression was associated with poor survival in patients with lung adenocarcinoma. The PD-L1/programmed cell death 1 pathway may contribute to the progression of smoking-associated tumors in lung adenocarcinoma.
Methods
The expression of PD-L1 protein in 417 surgically resected primary lung adenocarcinomas was evaluated by immunohistochemical analysis. The cutoff value for defining PD-L1 positivity was determined according to the histogram of proportions of PD-L1-positive cancer cells.
Results
Samples from 85 patients (20.4%) and 144 patients (34.5%) were positive for PD-L1 protein expression according to 5% and 1% PD-L1 cutoff values, respectively. Fisher's exact tests showed that PD-L1 positivity was significantly associated with male sex, smoking, higher tumor grade, advanced T status, advanced N status, advanced stage, the presence of pleural and vessel invasions, micropapillary or solid predominant histological subtypes, and wild-type EGFR. Univariate and multivariate survival analyses revealed that patients with PD-L1 positivity had poorer prognoses than those without PD-L1 protein expression at the 1% cutoff value (disease-free survival p < 0.0001, overall survival p < 0.0001). Conclusions: PD-L1 protein expression was significantly higher in smoking-associated adenocarcinoma and in EGFR mutation-negative adenocarcinoma. PD-L1 protein expression was associated with poor survival in patients with lung adenocarcinoma. The PD-L1/programmed cell death 1 pathway may contribute to the progression of smoking-associated tumors in lung adenocarcinoma.