De-differentiation of papillary thyroid carcinoma into squamous cell carcinoma. A case of coexistence within an excised neck lesion.

An 80-year-old man with papillary thyroid carcinoma of the neck underwent surgery and radioiodide therapy. He presented 11 years later with a lesion adjudged from fine needle aspiration to be a squamous cell carcinoma (SCC). Histological analysis of the excised mass revealed a lymph node overwhelmed with papillary thyroid carcinoma and moderately differentiated SCC thought to have transformed from papillary cells. A very small number of similar transformations specifically involving the 'tall cell variant' of papillary carcinoma transforming to spindle cell carcinoma have been reported previously. This case report demonstrates clear images of this rare occurrence and briefly considers factors leading to de-differentiation. The clinician should consider possible transformation from papillary thyroid cancer in cases of SCC of the head and neck as this variation may be more aggressive.