PDL-1 expression in oral squamous cell carcinoma and implications for treatment.

Abstract

82 Background: PDL-1 expression has been shown in multiple tumours to be a key factor in treatment response and immunogenicity. In oral squamous cell carcinoma (OSCC), its role is controversial; the expression levels, prognostic significance and therapeutic relevance are unclear. This study was performed to determine the incidence of PDL-1 expression in OSCC, and to determine its correlation with demographic, clinical and pathological features, recurrence and survival. Methods: PDL1 expression levels were determined by immunohistochemistry (DAKO kit) on 64 samples of OSCC obtained during resection on tumour (T) and tumour infiltrating lymphocytes (TILs). Statistical analysis was performed for corelation with clinicopathological features and survival. We also analysed PD1/PDL1 expression on the mRNA-seq data from The Cancer Genome Atlas (TCGA) (n = 527) and Gene Expression Omnibus (GEO) (n = 61) for validation. Results: PDL1 expression of < 1% was the most common for T (92%) and TILs (56%). Tumour PDL-1 expression < 1% had higher lymphovascular invasion (LVI) (p = 0.044) and bone invasion (p = 0.010). TIL PDL-1 expression < 1% was more common in patients < 45 years (p = 0.023) with more local recurrences (p = 0.020). For TCGA data, overall survival (OS) in the young ( < 45 years) was reduced in patients with low ( < 1%) PD1 expression (p = 0.010) while GEO data showed that older patients ( > 45 years) had a significantly higher PD1 expression level (p = 0.044). Conclusions: PDL1 expression in OSCC was low. Low TIL PDL1 expression was more common in patients with age < 45 years, with a higher chance of local recurrence. Genomic data also validated a potential link between PD1 expression and age. On the tumour, PD1 expression may be an important prognosticator, while on TILs, PDL1 is likely more relevant. Moreover PDL1 expression on the tumour is likely to be heterogeneous, so TIL PDL1 expression may be more representative of the tumour microenvironment and a better prognostic marker.