RESUMEN
Primary squamous cell carcinoma of the thyroid gland is very rare and its histogenesis is poorly defined so far. Although there have been some cases of squamous cell carcinoma with variant types of papillary thyroid carcinoma (PTC), the present case is the first primary squamous cell carcinoma with classic PTC to be reported. A 43-year-old woman presented with a 20 year history of neck mass. Neck ultrasound indicated a 6x4x3 cm large mass. The patient underwent total thyroidectomy. Histopathology indicated a well-differentiated squamous cell carcinoma and squamous metaplasia in conjunction with classic PTC. On immunohistochemistry cytokeratin 7 was positive in papillary carcinoma and squamous metaplasia, thyroglobulin was positive only in papillary carcinoma, and p63 was positive in squamous metaplasia and squamous cell carcinoma. Postoperatively, the patient received 59.4 Gy adjuvant radiotherapy, hormonal therapy and radioactive iodine therapy. At 8 months after surgery the patient remained disease free.