Papillary Thyroid Carcinoma With Squamous Dedifferentiation: A Potential Diagnostic Pitfall

Abstract Background/Aim: Squamous cell carcinoma (SCC) of the thyroid is a rare variant of the primary thyroid neoplasm, and some of such cases may involve dedifferentiation from papillary thyroid carcinoma (PTC). Case Report: We herein present a case of 76-year-old male who initially presented with dysphagia and weight loss. His imaging studies revealed a hypopharyngeal mass and bilateral thyroid nodules. Upon surgical resection, the right pyriform sinus mass showed typical histomorphology of a moderately differentiated SCC, whereas the right peritracheal mass revealed histomorphology of a conventional PTC. The right pyriform sinus SCC demonstrated positive immunoreactivity of PAX8, supporting its thyroid origin. One of two paratracheal lymph nodes was positive for metastatic SCC and PTC, respectively. Conclusion: This report highlights a rare case of SCC arising from PTC dedifferentiation. The clinical course, imaging and histopathological evaluation, and a review of literature are presented. Due to its rarity, this could present as a clinical dilemma. Improving awareness of this rare entity with the clinic-histopathological correlation will lead to correct diagnosis and optical treatment.