Abstract

Squamous metaplasia (SM) in the thyroid is uncommon and may occur in both non-neoplastic and neoplastic conditions, requiring distinction from papillary thyroid carcinoma with squamous differentiation (PTC-SD) and primary or metastatic squamous cell carcinoma (SCC). Case report: We report a case of papillary thyroid carcinoma with extensive SM (PTC-SM) in a 47-year-old female presenting with a right thyroid nodule (ACR TI-RADS V). No lesions were found in adjacent organs. Fine-needle aspiration confirmed PTC, and total thyroidectomy was performed. Histopathology revealed classic PTC with multiple foci of squamoid differentiation without cytological atypia. Immunohistochemistry showed CK7, CK19 and p63 positivity in both components, p63 positivity limited to squamous areas, and TTF- 1 and CK20 negativity in squamous cells. A diagnosis of PTC-SM was established. Conclusion: Although rare, SM may pose diagnostic challenges. It does not appear to affect prognosis but must be distinguished from aggressive variants and SCC for appropriate management.