We report the first case of squamous cell carcinoma (SCC) of the thyroid gland coexisting with papillary thyroid carcinoma (PTC) and Hashimoto's thyroiditis and discuss various theories concerning the histogenesis of SCC of the thyroid gland and the optimal treatment strategy.

A 54-year-old woman presented with an anterior neck mass measuring 4cm on clinical examination. Imaging showed a suspicious thyroid nodule invading the trachea. Total thyroidectomy with bilateral central lymph node resection was performed. Histological examination revealed tall cell variant of papillary thyroid carcinoma associated with SCC of the right lobe of the thyroid and Hashimoto's thyroiditis. Immunohistochemistry of the SCC showed positive staining for p53 and Ki67 and negative staining for thyroglobulin. The patient underwent adjuvant radioactive iodine therapy and radiotherapy. With postoperative follow-up of 24 months, the patient was in good health.

In conclusion, the most probable origin of SCC in this case was malignant transformation from Hashimoto's thyroiditis following a phase of metaplasia. This immunohistological profile is associated with a better prognosis. Optimal treatment consists of extensive surgical resection of tumour tissuefollowed by radiotherapy.