| Summary: | Although lung adenocarcinomas (LADs) with ground-glass opacity (GGO; part-solid tumors) have been shown to differ from those without GGO (pure-solid tumors) in clinicopathological features and prognoses, whether programmed death ligand-1 (PD-L1) protein expression differs between these two tumor types is unclear. This study included 124 patients with clinical T1a−c LAD who received pulmonary resections during 2007−2009. The E1L3N antibody was used to stain for PD-L1 in primary LAD specimens. The specimens were considered PD-L1<sup>+</sup> if ≥1% of tumor cells showed membrane staining, and were classified as having a high PD-L1<sup>+</sup> tumor proportion score (TPS) if ≥50% of the tumor cells did so. Among the 124 patients, 45 had part-solid tumors and 79 had pure-solid tumors. These two groups did not significantly differ in terms of clinical factors. However, the rates for PD-L1 positivity (4% vs. 25%, <i>p</i> < 0.01) and high PD-L1<sup>+</sup> TPS (2% vs. 16%, <i>p</i> = 0.02) were significantly higher in the pure-solid tumors. The multivariate analyses (logistic regression model) showed that the odds ratios for PD-L1 positivity and high PD-L1<sup>+</sup> TPS in pure-solid LADs were 5.9 (95% CI; 1.2−29.7) and 8.0 (95% CI; 1.0−63.8), respectively. In conclusion, LADs with GGO were correlated with a lower incidence of PD-L1 expression than pure-solid tumors.
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