[1115] Anaplastic and Squamous Thyroid Carcinoma Masquerading as Primary Mucosal Squamous Cell Carcinoma of the Trachea: Morphologic and Immunohistochemical Findings

NM Banville, CI Timon, NJ Bermingham, ME Toner. St James Hospital, Dublin 8, Ireland; Trinity College, Dublin 2, Ireland; Dublin Dental Hospital, Trinity College, Dublin 2, Ireland

Background: Involvement of the larynx or trachea by thyroid carcinoma is not rare but, in well differentiated tumors, the origin is usually apparent, based on the tumor morphology. We report a series of 6 patients with anaplastic or squamous thyroid carcinoma in whom the presenting features related to a tracheal mass, and in which the biopsy showed what appeared to be primary mucosal squamous cell carcinoma (SCC).
Design: We examined the morphology of the tumours and adjacent epithelium, and expression of cytokeratins 7, 5&6, 19, thyroid transcription factor 1 (TTF1) and thyroglobulin (TG) by immunohistochemistry (all antibodies: DAKO).
Results: Five cases were anaplastic carcinoma with both spindle and squamous differentiation, 2 with coexistent well differentiated carcinoma (2 papillary,1 follicular). The sixth case was a squamous cell carcinoma of thyroid. In 5 of the 6 cases, the SCC appeared to arise within dysplastic squamous epithelium, mimicking a primary mucosal carcinoma. The tracheal component showed cytokeratin 7 positivity in 4 of 4 (focal), TTF1 (positivity in 1 of 4 (focal), and TG positivity (focal) in 1 of 4. Cytokeratin 19 was positive in 4 of 4 (focal). Cytokeratin 5&6 was positive to a varying extent in all cases.
Conclusions: Anaplastic and squamous cell thyroid carcinoma invading the trachea may mimic a primary mucosal squamous cell carcinoma, even appearing to arise from dysplastic tracheal epithelium. Immunohistochemistry is of limited value in clarifying the diagnosis, although TTF1 and TG may show focal positivity.
Category: Head & Neck

Monday, March 9, 2009 1:00 PM

Poster Session II # 180, Monday Afternoon