Tumour-Infiltrating Lymphocytes (TILs) and PD-L1 Expression Correlate with Lymph Node Metastasis, High-Grade Transformation and Shorter Metastasis-Free Survival in Patients with Acinic Cell Carcinoma (AciCC) of the Salivary Glands

• Main Authors: Selina Hiss, Markus Eckstein, Patricia Segschneider, Konstantinos Mantsopoulos, Heinrich Iro, Arndt Hartmann, Abbas Agaimy, Florian Haller, Sarina K. Mueller
• Format: Article
• Language: English
• Published: MDPI AG 2021-02-01
• Series: Cancers
• Subjects: PD-L1; tumour-infiltrating lymphocytes; checkpoint inhibition; immuno-oncology; acinic cell carcinoma
• Online Access: https://www.mdpi.com/2072-6694/13/5/965

Objectives: The aim of this study was to assess the number of tumour-infiltrating lymphocytes (TILs) and the expression of <i>Programmed Cell Death 1 Ligand 1</i> (PD-L1) in Acinic Cell Carcinoma (AciCC) of the salivary glands, to enable a correlation with clinico-pathological features and to analyse their prognostic impact. Methods: This single centre retrospective study represents a cohort of 36 primary AciCCs with long-term clinical follow-up. Immunohistochemically defined immune cell subtypes, i.e., those expressing T-cell markers (CD3, CD4 and CD8) or a B-cell marker (CD20) were characterized on tumour tissue sections. The number of TILs was quantitatively evaluated using software for digital bioimage analysis (QuPath). PD-L1 expression on the tumour cells and on immune cells was assessed immunohistochemically employing established scoring criteria: tumour proportion score (TPS), Ventana immune cell score (IC-Score) and combined positive score (CPS). Results: Higher numbers of tumour-infiltrating T- and B- lymphocytes were significantly associated with high-grade transformation. Furthermore, higher counts of T-lymphocytes correlated with node-positive disease. There was a significant correlation between higher levels of PD-L1 expression and lymph node metastases as well as the occurrence of high-grade transformation. Moreover, PD-L1 CPS was associated with poor prognosis regarding metastasis-free survival (<i>p</i> = 0.049). Conclusions: The current study is the first to demonstrate an association between PD-L1 expression and lymph node metastases as well as grading in AciCCs. In conclusion, increased immune cell infiltration of T and B cells as well as higher levels of PD-L1 expression in AciCC in association with high-grade transformation, lymph node metastasis and unfavourable prognosis suggests a relevant interaction between tumour cells and immune cell infiltrates in a subset of AciCCs, and might represent a rationale for immune checkpoint inhibition.