Tumour infiltrating lymphocytes in oropharyngeal carcinoma: prognostic value and evaluation of a standardised method.

Tumour infiltrating lymphocytes (TILs) have been described as a biomarker for the host immune response against the tumour with prognostic properties. The International Immuno-Oncology Biomarkers Working Group (IBWG) proposed a standardised method for quantifying TILs in solid tumours to improve consistent and reproducible scoring. In this study, the methodology was tested in a retrospective population of oropharyngeal squamous cell carcinoma (OPSCC). TIL quantification was performed on 92 OPSCC samples (2004-2013) by four independent observers as described by the IBWG. Interobserver variability was assessed and results were correlated with clinicopathological variables and survival. TIL evaluation turned out to be challenging in OPSCC due to heterogeneity of TILs distribution, presence of pre-existing lymphoid tissue, surface ulceration or erosion and insufficient amount of intertumoural stroma in biopsies. Nonetheless, interobserver variability proved to be good to excellent. High stromal TILs (TILstr) and intratumoural TILs (TILtum) were both correlated to favourable overall survival and multivariate analysis showed TILstr to be the sole independent prognostic factor in OPSCC. The IBWG-proposed TIL quantification method is feasible and reproducible in OPSCC and provides valuable prognostic information regarding clinicopathological characteristics and overall survival. The use of this standardised methodology may facilitate implementation of TILs scoring as a prognostic biomarker in OPSCC.