Squamous-cell carcinoma of the thyroid
Other names	Thyroid squamous-cell carcinoma, squamous-cell thyroid carcinoma
Micrograph of squamous-cell carcinoma (H&E stain)
Specialty	Oncology

Squamous-cell carcinoma of the thyroid (SCT), or thyroid squamous-cell carcinoma, is rare malignant neoplasm of thyroid gland which shows tumor cells with distinct squamous differentiation. The incidence of SCT is less than 1% out of thyroid malignancies.^[1]

Squamous epithelial cells are not found in a normal thyroid, so the origin of SCT is not clear. However, it might be derived from embryonic remnants such as thyroglossal ducts or branchial clefts. Often, SCT is diagnosed in one of the thyroid lobes but not in the pyramidal lobe. Another possible way of developing SCT is through the squamous metaplasia of cells. However, that theory is also controversial since Hashimoto's thyroiditis and chronic lymphocytic thyroiditis (neoplasms to be shown^{[clarification needed]} squamous metaplasia) are not associated with SCT. Primary STC is usually diagnosed in both lobes of the thyroid gland. The histopathology of STC shows a squamous differentiation of tumor cells.

Squamous-cell carcinoma of the thyroid is biologically aggressive malignant neoplasm which is associated with rapid growth of neck mass followed by infiltration of thyroid-adjacent structures. Patients usually demonstrate dysphagia, dyspnea and voice changes, as well as local pain in the neck.

The tools required to diagnosis primary squamous cell carcinoma of the thyroid are panendoscopy, CT-Scan or PET-CT and immunohistological analysis. ^[2]

Thyroidectomy and neck dissection show good results in early stages of SCT. However, due to highly aggressive phenotype, surgical treatment is not always possible. The SCT is a radioiodine-refractory tumor. Radiotherapy might be effective in certain cases, resulting in relatively better survival rate and quality of life. Vincristine, doxorubicin and bleomycin are used for adjuvant chemotherapy, but their effects are not good enough according to publications.

Squamous-cell carcinoma of the thyroid exhibits a highly aggressive phenotype, thus prognosis of that malignancy is extremely poor. The overall survival is less than 1 year in most of cases.^[3]