title: Napsin A expression in anaplastic, poorly differentiated, and micropapillary pattern thyroid carcinomas.
abstract: Napsin A is a sensitive and specific marker for pulmonary adenocarcinoma versus squamous cell carcinoma. However, studies have shown that napsin A is also positive in approximately 5% of papillary thyroid carcinomas. The prevalence of napsin A in more aggressive types of thyroid carcinoma is unknown. Napsin A positivity in metastatic thyroid carcinoma, especially in conjunction with thyroid transcription factor-1 (TTF-1), could be misdiagnosed as lung adenocarcinoma. We investigated napsin A, TTF-1, and PAX8 expression in 26 anaplastic, 16 poorly differentiated, and 2 micropapillary pattern thyroid carcinomas. A focal micropapillary component was also present in 3 poorly differentiated and 3 anaplastic thyroid carcinomas. Four of 26 (15%) anaplastic, 2/16 (13%) poorly differentiated, and 2/2 (100%) micropapillary pattern thyroid carcinomas were napsin A positive. Three of the 6 cases (50%) with a focal micropapillary component were napsin A positive (1 of these 3 cases was positive only in the micropapillary component). All napsin A-positive cases were also positive for TTF-1, and all but 1 micropapillary pattern carcinoma were also PAX8 positive. In 1 case, napsin A was positive in the micropapillary component, but PAX8 was only positive in the adjacent poorly differentiated carcinoma. In summary, a minority of anaplastic and poorly differentiated thyroid carcinomas are napsin A positive. More importantly, napsin A expression is more common in carcinomas with a micropapillary component, a pattern shared in common with some lung adenocarcinomas. PAX8 may be diagnostically useful to distinguish these napsin A-positive thyroid carcinomas from lung adenocarcinomas, which are PAX8 negative.
authors.affiliation: Department of Pathology and Immunology, Washington University School of Medicine, St Louis, MO, USA. rchernock@path.wustl.edu
authors.forename: Rebecca D
authors.initials: RD
authors.lastname: Chernock
authors.forename: Samir K
authors.initials: SK
authors.lastname: El-Mofty
authors.forename: Nils
authors.initials: N
authors.lastname: Becker
authors.forename: James S
authors.initials: JS
authors.lastname: Lewis
mesh_terms: D000230:Adenocarcinoma / Q000201:enzymology / Q000473:pathology; D000077192:Adenocarcinoma of Lung; D016282:Aspartic Acid Endopeptidases / Q000032:analysis*; D014408:Biomarkers, Tumor / Q000032:analysis*; D001706:Biopsy; D002291:Carcinoma, Papillary / Q000201:enzymology* / Q000473:pathology*; D002454:Cell Differentiation; D004268:DNA-Binding Proteins / Q000032:analysis; D003937:Diagnosis, Differential; D006801:Humans; D007150:Immunohistochemistry; D008175:Lung Neoplasms / Q000201:enzymology / Q000473:pathology; D000072636:PAX8 Transcription Factor; D051761:Paired Box Transcription Factors / Q000032:analysis; D011237:Predictive Value of Tests; D065646:Thyroid Carcinoma, Anaplastic; D013964:Thyroid Neoplasms / Q000201:enzymology* / Q000473:pathology*; D014157:Transcription Factors
chemical_list: D014408:Biomarkers, Tumor; D004268:DNA-Binding Proteins; D000072636:PAX8 Transcription Factor; C083325:PAX8 protein, human; D051761:Paired Box Transcription Factors; C504003:TTF1 protein, human; D014157:Transcription Factors; D016282:Aspartic Acid Endopeptidases; C498549:NAPSA protein, human