[PD-L1 expression in primary non-small cell lung cancer and paired brain metastasis: consistency and clinical implications].

Objective To investigate the concordance of programmed death ligand-1 (PD-L1) expression between primary non-small cell lung cancer (NSCLC) and paired brain metastasis, analyze its relationship with clinicopathological characteristics, and evaluate the feasibility of using primary tumor PD-L1 status to predict brain metastasis status. Methods Thirty-two paired primary NSCLC and brain metastasis samples, pathologically diagnosed between January 1, 2017 and July 1, 2022, were collected. PD-L1 expression was detected by immunohistochemistry and interpreted using the Tumor Proportion Score (TPS), with cut-off values set at 1% and 50%. The Chi-square test was used to analyze the relationship between PD-L1 expression and clinicopathological features. Paired Chi-square and Kappa consistency tests were employed to assess the concordance of PD-L1 expression between primary and metastatic sites. Results PD-L1 expression showed no significant correlation with patient gender, age, treatment history, or histologic type. At the 1% cut-off, the overall PD-L1 expression showed moderate concordance between primary and metastatic sites (Kappa=0.624). Subgroup analysis revealed high concordance in untreated patients (Kappa=0.761, P=0.001), whereas the treated group showed weak concordance without statistical significance (Kappa=0.324, P=0.205). At the 50% cut-off, both the treatment group and the untreated group showed weak concordance without statistical significance. Although the chemotherapy subgroup showed perfect agreement (Kappa=1.000) at the 50% cut-off, the high-expression concordance rate was only 20.00%, indicating limited clinical reference value. Conclusion The strong concordance of PD-L1 expression in the untreated group patients supports the use of primary tumor PD-L1 status to guide clinical decision-making when brain metastasis tissue is unavailable. Treatment status (mainly including chemotherapy) may be an important factor affecting the consistency of high PD-L1 expression between primary NSCLC and brain metastasis.