Anaplastic thyroid carcinoma presenting as laryngotracheal invasive squamous cell carcinoma: A report of two cases and review of the literature

Anaplastic thyroid carcinoma (ATC), one of the most aggressive subtypes of thyroid cancer, is composed of undifferentiated thyroid follicular cells demonstrating ultrastructural or immunohistochemical features of epithelial differentiation. Frequently, these tumors can be shown to have originated from papillary thyroid carcinoma (PTC). ATC exists on a morphologic spectrum composed of three main patterns: spindle cell (sarcomatoid), giant cell, and epithelial (squamous) components.