RESUMO
Thyroid cancer is a common malignancy worldwide, and its incidence is increasing rapidly, especially in women. In the majority of cases, it presents solely with a palpable neck swelling. Less commonly, the disease manifests with symptoms of advanced stages, such as superior vena cava (SVC) obstruction and indications of recurrent laryngeal nerve invasion. Anaplastic thyroid cancer is a rare variant of thyroid cancer and is considered to have one of the poorest prognoses, and its diagnosis and treatment are challenging. On the other hand, undifferentiated pleomorphic sarcoma is a differential diagnosis with many clinical and histological similarities, which can only be confirmed through immunohistochemical studies. We herein report a challenging case of a 69-year-old female patient who presented with obstructive symptoms, diagnosed with anaplastic thyroid cancer exhibiting unusual clinical and histological features.