Hashimoto's thyroiditis with papillary thyroid carcinoma (PTC)-like nuclear alterations express molecular markers of PTC

Focal papillary thyroid carcinoma (PTC)-like nuclear alterations have been documented in Hashimoto's thyroiditis; however, the molecular association between PTC and Hashimoto's thyroiditis is poorly understood. The aim of this study was to determine whether molecular expression patterns of PTC are present in association with PTC-like nuclear alterations in Hashimoto's thyroiditis.The expression of four genes known to be up-regulated in PTC [LGALS3 (galectin3), CITED1, KRT19 (cytokeratin 19) and FN1 (fibronectin-1)] and the human mesothelial cell protein identified by monoclonal antibody HBME1 was evaluated. Immunohistochemistry was performed on 23 cases of Hashimoto's thyroiditis with focal or diffuse Hürthle cell change and PTC-like nuclear alterations, 37 PTC and 18 normal thyroids. Focal expression of galectin3 (GAL3), CITED1, cytokeratin 19 (CK19), HBME1 and fibronectin-1 (FN1) was seen in 87%, 65%, 43%, 26% and 17% of Hashimoto's thyroiditis, respectively, only in thyrocytes showing PTC-like nuclear alterations. In contrast, diffuse expression of GAL3, CITED1, CK19, HBME1 and FN1 was seen in 100%, 95%, 70%, 87% and 89% of PTC, respectively. Normal thyroid tissues did not express any of these proteins. Following immunohistochemistry, four Hashimoto's thyroiditis cases were found to contain foci of PTC. These foci were highlighted by the diffuse and strong expression of PTC-associated proteins, which prompted additional retrospective scrutiny of the haematoxylin and eosin-stained sections leading to appreciation of complete PTC-type nuclear atypia.Focal PTC-like immunophenotypic changes in Hashimoto's thyroiditis suggest the possibility of early, focal premalignant transformation in some cases of Hashimoto's thyroiditis.