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.Here we discuss two cases in which patients presented with upper airway symptoms and subsequently, a laryngotracheal lesion was detected by imaging studies and bronchoscopy. In each case, biopsies taken from these lesions showed invasive squamous cell carcinoma; however, both patients had previously undergone total thyroidectomy for PTC, and immunohistochemical studies revealed that the biopsied tumor cells were of thyroid origin. Furthermore, the cells harbored the BRAFV600E mutation, suggesting anaplastic transformation from PTC.Invasion into the larynx or trachea is a known complication of aggressive forms of thyroid cancer. However, laryngotracheal presentation of anaplastic thyroid carcinoma with squamous differentiation can easily be misdiagnosed as a primary squamous cell carcinoma. Immunohistochemical studies for thyroid lineage markers (e.g. PAX8) as well as squamous markers (e.g. p40, p63) should be performed, and if there is a known history of PTC, mutation analysis for BRAFV600E can support the diagnosis via molecular testing or immunohistochemistry.