[Programmed death ligand 1 expression and CD8⁺T lymphocyte infiltration in salivary gland lymphoepithelial carcinoma]

Objective: To study the expression of programmed death ligand-1 (PD-L1) in tumor cells and CD8⁺T lymphocytes in tumor infiltrating lymphocytes, and to analyze the correlation of PD-L1 expression with infiltration of CD8⁺T lymphocytes and clinicopathologic features in salivary gland lymphoepithelial carcinoma (LEC). Methods: Forty-two cases of primary salivary LECs and 21 cases of secondary salivary LECs were enrolled at the Department of Oral Pathology, Shanghai Ninth People's Hospital, Shanghai Jiaotong University between 2015 and 2017. The expression of Epstein-Barr (EB) virus, PD-L1 and CD8 was examined using chromogenic in situ hybridization (CISH) and immunohistochemistry (IHC) staining. The data were analyzed using SPSS 23.0 software package. Results: EB virus was detected in 61 cases (61/63, 96.8%), including 42 (42/42, 100%) primary LECs and 19 (19/21, 90.5%) secondary LECs. The PD-L1 positive rate (score ≥1) was 97.6% (41/42), and its high-expression rate (score ≥20) was 78.6% (33/42) in primary LECs. The PD-L1 positive rate (score ≥1) was 71.4% (15/21), and its high-expression rate (≥20) was 38.1% (8/21) in secondary LECs. However, the PD-L1 positive rate (score ≥1, P=0.004) and high-expression rate (score ≥20, P=0.001) in primary LECs were higher than those in secondary LECs. There was no difference in the infiltration degree of CD8⁺T lymphocytes between primary and secondary LECs. There was a significant correlation between the expression of PD-L1 and CD8 in primary LECs (P=0.001) and in secondary LECs (P=0.048), respectively. Conclusions: There is PD-L1 expression in primary and secondary salivary LECs, while the expression rate is higher in primary LECs than secondary LECs. The combination of PD-L1 expression and CD8⁺T lymphocytes' presence suggest that most LEC patients might be responsive to immunotherapy, and primary LECs might be more significantly responsive than secondary LECs.