PD-L1 and PD-1 expression in thyroid follicular epithelial dysplasia: Hashimoto thyroiditis related atypia and potential papillary carcinoma precursor.

Programmed cell death ligand (PD-L1)/PD-1 expression has been studied in a variety of cancers and blockage of PD-L1/PD-1 pathway is a cornerstone of immunotherapy. We studied PD-L1/PD-1 immunohistochemical expression in 47 thyroid gland specimens in groups of (1) Hashimoto thyroiditis (HT) only; (2) HT and follicular epithelial dysplasia (FED); and (3) HT, FED, and papillary thyroid carcinoma (PTC). PD-1 positivity was found in immune cells, namely in lymphocytes, macrophages, and plasma cells with mean values for lymphocytes and macrophages 9% in HT group, 4% in FED group, and 4% in PTC group.