The impact of concurrent autoimmune thyroid disease on the tumour microenvironment and disease progression in papillary thyroid cancer (PTC) is not well understood. Studies evaluating the programmed cell death ligand 1 (PD-L1) tumour expression in PTC have shown variable results, and the effect of lymphocytic thyroiditis (LT) on tumour PD-L1 expression has not been adequately assessed. The main aim of this study was to determine expression of PD-L1 in PTC with and without LT. We examined 81 PTC cases; 28.5% of all reviewed PTC had presence of LT. In PTC specimens without LT, tumour PD-L1 expression was significantly lower compared to PD-L1 expression in PTC with LT, 6.9% vs 39.1%, respectively. Expression of PD-L1 did not differ with PTC stage, even when sub-categorised according to the presence and absence of LT. Utility of PD- L1 expression as a prognostic marker in thyroid cancer needs to be interpreted with caution.
Keywords: PD-L1; Papillary thyroid cancer; lymphocytic thyroiditis; programmed cell death ligand 1; tumour microenvironment.
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