PD-L1 expression on tumor cells and tumor-infiltrating immune cells in thymic epithelial tumors detected with SP142 and SP263 antibodies.

Abstract

Introduction: Programmed death-ligand 1 (PD-L1) expression in various tumors is known to correlate with the efficacy of immune checkpoint inhibitors; however, evaluation of PD-L1 expression in thymic epithelial tumors (TETs) using multiple antibodies are limited. We retrospectivity evaluated PD-L1 expression in thymomas and thymic carcinomas using two antibodies, SP142 and SP263, and compared their expression rates in each type of TETs.

Materials and methods: We retrospectively included 37 cases of thymoma and 11 cases of thymic carcinoma that were histologically diagnosed between January 2000 and December 2020. PD-L1 expression was assessed using SP142 and SP263 antibodies with semi-quantitative scoring.

Results: The concordance rate for PD-L1 positivity between SP142 and SP263 was 81.2%, whereas the concordance rate for high PD-L1 expression was 83.3%. SP142 showed positive PD-L1 expression in 23 (62%) thymoma cases and eight (73%) thymic carcinoma cases. In contrast, SP263 antibody showed positive PD-L1 expression in 31 (84%) cases of thymoma and 9 (82%) cases of thymic carcinoma. In addition, type B thymomas exhibited significantly higher PD-L1 positivity than other thymoma types. The tumor-infiltrating lymphocytes were mostly CD3 and CD8 positive. No significant difference in overall survival was observed between the high and low PD-L1 expression groups in thymic carcinoma.

Conclusion: PD-L1 expression rate was high in TETs, with variations depending on the antibody used and histological subtype. SP263 showed higher PD-L1 expression compared to SP142. The type of the antibody used should be considered when evaluating PD-L1 expression in TETs.