An immunohistochemical analysis of PD-L1 protein expression in surgically resected small cell lung cancer using different antibodies and criteria

Background: Programmed cell death ligand 1 (PD-L1) expression in lung cancer appears to be important in immunotherapy, as its expression can predict responses to programmed cell death-1 (PD-1)-blocking antibodies. However, a definitive antibody and cut-off value for PD-L1 expression are urgently needed. Materials and Methods: The PD-L1 expression in 40 surgically resected small cell lung cancer (SCLC) specimens was evaluated by immunohistochemistry (IHC) with three different antibodies: clones E1L3N, 28-8, and SP142, and using three different evaluations: the Allred score, 1% cut-off, and 5% cut-off. Results: The percentage of tumors with positive PD-L1 expression was inconsistent in the IHC evaluations using the Allred score and 1% cut-off. However, the IHC evaluations using the 5% cut-off showed similar rates of expression using the three different antibodies. Conclusion: The results of this study provided detailed evidence on the frequency of PD-L1 expression in surgically resected SCLC, which may be a useful reference for identifying patients with PD-L1-expressing SCLC.