Anaplastic Thyroid Carcinoma with Rhabdomyoblastic Differentiation: A Case Report with a Good Clinical Outcome

Anaplastic thyroid carcinoma is a rare and highly malignant disease. Usually, this type of tumor is irresectable, and almost all patients die within 1 year after diagnosis. We present a case of anaplastic thyroid carcinoma with rhabdomyoblastic differentiation and good therapeutic outcome. A 76-year-old female was referred to our hospital with a growing, painless neck mass which existed for 3 months. Biopsy of the mass showed microscopically and immunohistochemically a follicular (Hürthle cell) carcinoma of the thyroid, dedifferentiated to an anaplastic carcinoma with divergent differentiation along rhabdomyoblastic cell lines. The patient underwent a total thyroidectomy with additional lymph node dissection, followed by two episodes of 150 mC I¹³¹ therapy and external radiotherapy. After a follow-up of 3 years, the patient still remains in a good condition without any signs of recurrent disease. Other cases of rhabdomyoblastic and rhabdoid anaplastic thyroid carcinomas have been described. Both types of carcinoma are associated with an aggressive clinical course. In our case, the patient is still alive without evidence of disease 3 years after primary therapy. The good clinical outcome of our patient suggests that surgical resection, radiotherapy, and I-131 ablation therapy with curative intent seems to be an adequate treatment option in patients with anaplastic thyroid carcinoma with rhabdoid and rhabdomyoblastic differentiation.