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

Abstract

e17527 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: PDL-1 IHC (Dako kit) was determined on 64 samples of OSCC obtained during curative intent resection. PDL-1 expression levels were determined in tumour (T) and tumour infiltrating lymphocytes (TILs). Statistical analysis was performed. Results were validated on the mRNA-seq data from the Cancer Genome Atlas (TCGA) for head and neck squamous cell carcinoma (HNSCC). Results: 64 patients were included in the final analysis with a mean age of 54 years. < 1% expression was the most common for T (92%) and TILs (56%). Tumour PDL-1 expression < 1% had higher risk of 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 higher chances of local recurrence (p = 0.020) and reduced local recurrence free survival (p = 0.047). For the TCGA data, low ( < 1%) PDL-1 expression was associated with a significant reduction in OS and DFS in the young (≤45 years) (p = 0.0078 and 0.0089 respectively), but not for older patients ( > 45 years) (p = 0.21 and 0.88 respectively). Conclusions: PDL-1 expression in OSCC was low. TIL PDL-1 expression < 1% was more common in those ≤45 years, and associated with a higher chance of local recurrence and poorer survival. The role of PDL-1 expression in prognosis of OSCC is controversial, with our data being the first to correlate low PDL-1 expression and poorer outcomes with younger patients. These results were validated by the TCGA data for HNSCC across multiple subsites. Further study is required to determine if this pathway plays a significant role in local control and survival.