Reduced HBME‐1 immunoreactivity of papillary thyroid carcinoma and papillary thyroid carcinoma‐related neoplastic lesions with Hürthle cell and/or apocrine‐like changes

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Abstract
Reduced HBME‐1 immunoreactivity of papillary thyroid carcinoma and papillary thyroid carcinoma‐related neoplastic lesions with Hürthle cell and/or apocrine‐like changes Background: We have recently observed that Hürthle cell tumours and papillary thyroid carcinoma with tumour cells showing decapitation of luminal portion of the cytoplasm (apocrine‐like changes) display negative or decreased immunoreactivity for HBME. The purpose of this study is to correlate papillary thyroid carcinoma with positive and negative immunoreactivity for HBME with the histopathological features. Methods and results: Two hundred and five thyroid neoplasms including carcinoma and adenomas were grouped into Hürthle cell tumours, tumours with or without some features of Hürthle cells, tumours with apocrine‐like changes and adenomas with or without limited nuclear features of papillary thyroid carcinoma but not diagnostic for papillary thyroid carcinoma. All neoplasms were submitted for immunostaining with cytokeratin 19 (CK19) and HBME. Papillary thyroid carcinoma, follicular carcinoma and follicular adenoma that have areas of limited nuclear features but not diagnostic for papillary thyroid carcinoma showed stronger immunostaining for HBME than their respective counterparts with Hürthle cell changes. All Hürthle cell tumours showed negative to focal reactivity. This decrease of reactivity for HBME was proportional to the levels of Hürthle cell changes. In addition, focal to extensive apocrine‐like changes were seen in most Hürthle cell neoplasms and rarely seen in non‐Hürthle cell neoplasms. Apocrine‐like changes abolished or decreased HBME immunoreactivity of papillary thyroid carcinoma and tumours with limited nuclear features. Immunostaining for cytokeratin AE3 was not affected by Hürthle cell or apocrine‐like changes. Conclusions: All papillary thyroid carcinomas without Hürthle cell or apocrine‐like differentiation are reactive for HBME. Hürthle cell tumours and tumours with Hürthle cell or apocrine‐like changes show negative or focal reactivity for HBME. Except for this limitation, HBME is a sensitive marker for papillary thyroid carcinoma and tumours with limited nuclear features.