Laryngotracheal presentation of anaplastic thyroid carcinoma with squamous differentiation: seven cases demonstrating an under‐recognized diagnostic pitfall

Aims To describe a series of anaplastic thyroid carcinomas that mimicked primary head and neck squamous cell carcinoma ( HNSCC ) by virtue of both morphology and clinical presentation. Methods and results Seven cases were identified in a 15‐year period where a biopsy of an airway lesion that appeared to be squamous cell carcinoma was, in fact, anaplastic thyroid carcinoma. The tumours had squamous and/or spindle cell morphology, with only the squamous component being apparent in the airway biopsy. Some tumours arose within metaplastic ( n  = 3) or atypical ( n  = 3) epithelium, supporting the diagnosis of a primary mucosal tumour. Positive PAX 8 ( n  = 5) and TTF ‐1 ( n  = 4) staining was identified. Conclusions An endotracheal presentation of anaplastic thyroid carcinoma with squamous morphology may be misdiagnosed as a primary head and neck squamous cell carcinoma. PAX 8 and TTF ‐1 expression are helpful in making the distinction, but the problem lies in suspecting a thyroid carcinoma in what appears to be a straightforward diagnosis of HNSCC .