An 82-year-old female patient presented herself at the PS-UNESP after a single episode of hemoptysis; there was a history of cough with whitish sputum for 6 months prior to that. Radiological examination revealed pulmonary lesions and the patient was admitted for investigation. Computerized tomography of the chest and neck revealed a mass in the left lobe and isthmus of the thyroid that was compatible with a neoplasm; in addition there were multiple pulmonary nodules suggestive of metastases. Bronchoscopy showed extrinsic compression of the trachea. Fine needle aspirates of nodules in both thyroid lobes were classified as Bethesda category V on cytopathological examination. Endocrinology evaluation was requested when the patient developed dyspnea at rest, orthopnea, paroxysmal nocturnal dyspnea, and edema of the lower limbs, along with progressive lesions on chest radiography. The patient gave a history of hoarseness, dysphagia, and odynophagia 5 years ago; these symptoms had partly improved over time. She also complained of weakness, hair loss, excessive sweating, and gradual weight loss over the past 6 years. Laboratory test results were as follows: TSH: 13.1 mU/L; Free T4: 1.25 ng/dL; anti-TPO-Ab: 8.55 IU/mL; anti-TG-Ab: 150.78 IU/mL; TG <0.2 ng/dL; CEA: 4.38 ng/mL; calcitonin <0.2 pg/mL; other laboratory test results were normal. The patient deteriorated clinically during investigation with worsening dyspnea that required supplemental oxygen. She could not be weaned from oxygen treatment, her level of consciousness deteriorated, and she died 8 days after admission to PS. The presence of pulmonary metastases suggested an aggressive thyroid carcinoma that could have been papillary, or poorly differentiated follicular, or anaplastic in type. Autopsy result was consistent with an anaplastic thyroid carcinoma with sarcomatoid foci with local spread to bilateral cervical lymph nodes and mediastinum and metastases to the lungs and spleen.