High expression of programmed cell death 1 ligand 1 in lung adenocarcinoma is a poor prognostic factor particularly in smokers and wild-type epidermal growth-factor receptor cases.

A clinical implication of programmed cell death 1 ligand 1 (PD-L1) expression in lung adenocarcinoma has not been well established. We evaluated PD-L1 expression immunohistochemically on 296 surgically resected lung adenocarcinomas to investigate a clinical implication of PD-L1 expression especially in terms of smoking history and epidermal growth-factor receptor (EGFR) mutation status. Patients were classified into high- and low-PD-L1 expression groups. The high-expression group (n = 107) showed a significantly higher proportion of smokers and poor differentiation compared with the low-expression group (n = 189). Survival analysis showed that the prognosis of the high-expression group was worse in overall survival than that of the low-expression group (3-year overall survival 85 vs. 94%, P = 0.005). Stratified survival analyses showed that the prognoses of the high-expression group were worse than those of the low-expression group in both strata of smokers and wild-type EGFR (P = 0.009 and P = 0.007, respectively). We found that high PD-L1 expression was a poor prognostic factor in the smokers or the patients with wild-type EGFR, whereas it was not the case in those who never smoked or those with EGFR mutation, implying the importance of adenocarcinoma driver mutations and etiology.