Primary undifferentiated pleomorphic sarcoma of the thyroid

RATIONALE Primary undifferentiated pleomorphic sarcoma is extremely rare in the thyroid, and can be easily misdiagnosed as anaplastic thyroid cancer. PATIENT CONCERNS We present a case of a 71-year-old woman who presented with a rapidly growing painless mass in the neck. DIAGNOSES-INTERVENTIONS-OUTCOMES Computed tomography showed a large hypointense mass with hyperdense areas involving whole of the right lobe of thyroid gland and fine-needle aspiration cytology found a few atypical cells. Surgical exploration was performed subsequently and frozen section showed malignant tumor. Therefore, a total thyroidectomy, central, and bilateral lateral neck dissection were performed and adjuvant radiotherapy of 60 Gy was administered. The patient was alive and had no recurrence at 6-month follow-up. LESSONS Although primary undifferentiated pleomorphic sarcoma in the thyroid is extremely rare, patients who presented with a rapidly growing painless mass in the neck should be considered and it is essential to excise the tumor completely as soon as possible.