Squamous cell carcinoma arising in thyroglossal duct remnant cyst epithelium.

The extremely rare occurrence of invasive squamous cell carcinoma arising from normal epithelial lining of a thyroglossal duct remnant cyst is documented by demonstrating the histopathologic transition from normal squamous epithelium to squamous cell carcinoma. The requirements that must be fulfilled to accept a lesion as arising de novo from the epithelial lining are outlined, and all requirements are achieved. The lesion is differentiated from the less rare papillary or papillary-follicular adenocarcinoma of residual thyroid tissue of the thyroglossal duct tract remnants. This is the sixth report in the world literature of invasive squamous cell carcinoma arising from benign thyroglossal remnant squamous epithelium, and the second demonstrating the transition from normal squamous epithelium to invasive squamous cell carcinoma.