Part of “CHAPTER 41 – UNUSUAL THYROID CANCERS“

Primary squamous cell carcinoma of the thyroid is defined by the WHO classification as a tumor comprised “entirely of cells showing so-called intracellular bridges and/or forming keratin.”1 The squamous cells are of uncertain origin.38 When this definition of “pure” squamous cell carcinoma is used, rather than that of tumors with an adenosquamous appearance or tumors with squamous metaplasia, the incidence is <1% of all thyroid malignancies.39 Before therapy, the clinician must be certain that the tumor does not represent metastases from head and neck or lung cancers.