Significance of PD-L1 expression in tongue cancer development

Aims: Immunohistochemistry of PD-L1 has been recently established as a surrogate method to predict if immunotherapy targeting PD-L1/PD-1 has a significant effect on suppression of cancers such as lung non-small cell carcinoma, melanoma, and renal cell carcinoma. Here we performed immunohistochemistry for PD-L1 expression in squamous cell carcinoma (SCC) of the tongue to investigate the potential correlation between PD-L1 expression and clinicopathological factors and whether PD-L1 expression would be associated with prognosis. Methods: Tissue microarray cores of paraffin-embedded blocks from 135 cases with surgically resected tongue SCC were immunohistochemically analysed for PD-L1 expression. Results: We observed a positive correlation between PD-L1 expression and tongue SCC pT1 and pT2 tumours, but a negative correlation with pT2, pT3 and pT4 tumours. We also observed a positive correlation with lymph node metastasis. However, no positive correlation was demonstrated between PD-L1 expression and overall survival. Conclusions: PD-L1 tends to be overexpressed at the early stage of tongue SCC, showing a close correlation with initial development of tongue. However, PD-L1 expression may not affect prognosis.