Expression of PD-L1 in pleural effusion of advanced lung adenocarcinoma and its relationship with DNA ploidy.

Objective: Programmed death receptor-1 (PD-1) negatively regulates antigen receptor signaling upon binding to its ligands, programmed death-ligand 1 or 2 (PD-L1/2), enabling tumor cells to evade immune surveillance. This study aimed to investigate the expression of PD-L1 in tumor cells present in pleural effusion (PE) from lung adenocarcinoma (LUAD) with metastasis and its relationship with DNA ploidy. Furthermore, it sought to assess whether high PD-L1 expression enhances tumor cell proliferation and invasiveness. Methodology: This was a retrospective study. PE specimens were collected from patients diagnosed with stage IV LUAD, meeting the malignant tumor UICC (Union for International Cancer Control) TNM staging system, at the Fourth Hospital of Hebei Medical University and Hebei Tumor Hospital between July 2021 to December 2023. The expression of PD-L1 in LUAD cells in PE was detected using immunocytochemistry, and the invasiveness of tumor cells with varying PD-L1 expression levels was evaluated through DNA quantitative analysis. Results: The positive expression rate of PD-L1 in PE from advanced LUAD was 60.22%. Variations in PD-L1 expression were associated with the mean DNA index values exceeding 2.5 among the top 20 tumor cells analyzed. Conclusion: Compared with the non-expression group, the low-expression PD-L1 group demonstrated greater tumor cell invasiveness.