PD-L1 Expression Evaluation in Lung Tumors

To evaluate PD-L1 expression, formalin-fixed paraffin-embedded samples of primary lung tumors were employed. Immunohistochemical staining was conducted utilizing the PD-L1 Clone 22C3 pharmDx Kit and Dako Automated Link 48 platform. The tumor proportion score (TPS) was defined as the percentage of cells with positive membrane staining after inspecting 100 viable cancer cells, which were categorized into three groups based on TPS values (TPS of 0%, 1–49% and ≥50%). The combined proportion score (CPS) was defined as expression of PD-L1 in both tumor and inflammatory cells, CPS was evaluated by the following formula: (PD-L1 positive tumor cells + PD-L1 positive inflammatory cells)/(total tumor cells) * 100, the optimal cut-off of PD-L1 CPS was unclear, we also categorized CPS into three groups (CPS of 0, 1–49, and ≥50) according to recent studies.^{14 (link),15 (link)}