Primary squamous cell carcinoma of the thyroid: immunohistochemical profile and literature review.

BACKGROUND Squamous cell carcinoma accounts for 1% of primary thyroid malignancies and is characterized by a rapidly unfavorable outcome. CASE PRESENTATION A 64-year-old woman presented with a painless mass in the left neck, coexisting with thyroid goiter. Total thyroidectomy with lymphadenectomy was performed and a primary thyroid squamous cell cancer was confirmed histologically after excluding any other possible primary malignancies. The tumor's immunohistochemical profile was explored using a large panel of antibodies. The tumor featured a positive immunoreaction to cytokeratins 7-19 and to squamous cell carcinoma antigen. Low-molecular-weight cytokeratins 5-6 and epithelial membrane antigen were also expressed. The neoplasm's proliferative index (Mib1) was 60%. No immunostaining was detected for cytokeratins 10-20, thyroglobulin, TTF-1, CD5, galectin-3 or p53. CONCLUSIONS This case of primary thyroid squamous cell carcinoma immunohistochemically profiled using a large panel of immunoreactions may offer useful information on the histological differentiation of thyroid squamous cell carcinoma from other (uncommon) thyroid carcinomas and the distinction between primary and secondary thyroid cancers.