Napsin A Expression in Anaplastic, Poorly Differentiated and Micropapillary Pattern Thyroid Carcinomas
Rebecca Chernock, Samir El-Mofty, Nils Becker, James Lewis, Jr.. Washington University School of Medicine, St Louis, MO
Background: Napsin A is more sensitive and specific for pulmonary adenocarcinoma versus squamous cell carcinoma than thyroid transcription factor-1 (TTF-1). TTF-1 is also a recognized marker of thyroid carcinomas. Preliminary studies have shown that napsin A is positive in ∼5% of papillary thyroid carcinomas as well. The prevalence of napsin A in anaplastic (ATC) and poorly differentiated (PDCa) thyroid carcinomas has not been thoroughly investigated. Napsin A positivity in metastatic thyroid carcinoma, especially in conjunction with TTF-1, could potentially be misdiagnosed as a lung metastasis. The aim of this study is to investigate the prevalence of napsin A expression in ATC, PDCa and the recently described micropapillary pattern (MPP) thyroid carcinoma, which show histologic similarity to a subset of lung adenocarcinomas.
Design: Immunohistochemistry for Napsin A, TTF-1 and PAX-8 was performed. Staining strength (weak, moderate or strong) and extent (1+ = 1-25%, 2+ = >25-50%, 3+ = >50-75%, 4+ = >75%) were evaluated.
Results: Twenty-six ATCs (21 primary, 4 regional lymph node metastases, 1 metastasis to larynx), as well as 16 PDCa (14 primary and 2 metastases—1 regional lymph node, 1 lung) and 2 MPP carcinomas (1 primary and 1 regional lymph node metastasis) were identified. A focal MPP component was seen in 3 PDCa and 3 ATCs. The immunohistochemistry results are summarized below:
|Histologic Type||Napsin A||TTF-1||PAX-8|