Immunophenotypic analysis of tumor infiltrating lymphocytes in Epstein-Barr virus-negative lymphoepithelial carcinoma of the oral cavity: Report of a case

Lymphoepithelial carcinoma (LEC) is a rare subtype of undifferentiated carcinoma with prominent lymphoid stroma consistently associated with Epstein-Barr virus (EBV) in Asian populations. We encountered a case of LEC of the floor of the mouth. In the present LEC, the EBV genome was not detected in tumor cells or tumor-infiltrating lymphocytes (TILs) by in situ hybridization. The invasive pattern of lymphoid infiltration in the present LEC was strongly characteristic. The TILs in this LEC were predominantly CD8+ and CD45RO+ T cells that invaded into and around tumor nests and islands. Moderate numbers of PD-1+ and FoxP3+ cells were also dispersed both within and between the tumor nests and islands. A profuse infiltrate of CD4+ T cells as well as some CD45RO+ T cells and a very few CD20+ B cells was mostly restricted to the tumor stroma. Membranous expression of PD-L1 on the tumor cells was not found in the entire lesion of the present LEC. These findings suggest that TILs in the present EBV-negative LEC might behave as tumor-suppressive immune cells in response to the invasion and proliferation of LEC.