title: PAX8 immunostaining of anaplastic thyroid carcinoma: a reliable means of discerning thyroid origin for undifferentiated tumors of the head and neck.
abstract: Anaplastic thyroid carcinoma can be difficult to diagnose because it does not show thyroid differentiation morphologically or immunohistochemically. Depending on the histologic variant, anaplastic thyroid carcinoma may be confused with sarcoma or squamous cell carcinoma of the head and neck. PAX8 is a transcription factor expressed in normal and neoplastic thyroid follicular epithelium and only a few other tissues. This restricted expression suggests that PAX8 staining could be useful when dealing with spindled or squamoid tumors of the neck. The purposes of this study were to determine the frequency of PAX8 staining in anaplastic thyroid carcinoma and to evaluate PAX8 immunohistochemistry as a means of distinguishing its squamoid variant from head and neck squamous cell carcinoma. PAX8 immunohistochemical staining was performed on 34 anaplastic thyroid carcinomas and 118 head and neck squamous cell carcinomas. PAX8 staining was present in 26 (76%) anaplastic thyroid carcinomas including 16 (100%) of 16 squamoid variants, 7 (58%) of 12 giant cell/pleomorphic variants, and 3 (50%) of 6 spindled variants. All head and neck squamous cell carcinomas were negative for PAX8. PAX8 expression is often retained in anaplastic thyroid carcinomas including the squamoid variant, but it is not expressed in head and neck squamous cancers. PAX8 staining is an excellent marker for carcinomas of follicular epithelial origin, including those carcinomas that are undifferentiated in other respects. The tissue specificity of PAX8 expression may be useful in resolving the differential diagnosis of anaplastic thyroid carcinoma such as the distinction between its squamoid variant and squamous cell carcinoma of the head and neck.
authors.affiliation: Department of Pathology, The Johns Hopkins Medical Institutions, Baltimore, Maryland, USA.
authors.forename: Justin A
authors.initials: JA
authors.lastname: Bishop
authors.forename: Rajni
authors.initials: R
authors.lastname: Sharma
authors.forename: William H
authors.initials: WH
authors.lastname: Westra
mesh_terms: D018263:Adenocarcinoma, Follicular / Q000378:metabolism / Q000473:pathology*; D014408:Biomarkers, Tumor / Q000378:metabolism; D002294:Carcinoma, Squamous Cell / Q000378:metabolism / Q000473:pathology; D003937:Diagnosis, Differential; D006257:Head / Q000473:pathology; D006801:Humans; D009333:Neck / Q000473:pathology; D009687:Nuclear Proteins / Q000378:metabolism; D009928:Organ Specificity; D000072636:PAX8 Transcription Factor; D051761:Paired Box Transcription Factors / Q000378:metabolism*; D065646:Thyroid Carcinoma, Anaplastic; D013961:Thyroid Gland / Q000378:metabolism / Q000473:pathology; D013964:Thyroid Neoplasms / Q000378:metabolism / Q000473:pathology*; D046888:Tissue Array Analysis
chemical_list: D014408:Biomarkers, Tumor; D009687:Nuclear Proteins; D000072636:PAX8 Transcription Factor; C083325:PAX8 protein, human; D051761:Paired Box Transcription Factors