A 32-year-old woman complains of tumor-like formation on the anterior surface of her neck that appeared 2 years ago. Within the last 3 months the tumor has been rapidly growing. It hinders swallowing and impairs speech; the tumor causes a sensation of pressure. Objectively the skin moisture is normal, pulse is 80/min., rhythmic, blood pressure is 130/80 mm Hg. In the right lobe of the thyroid gland there is a dense lumpy node 3.0×3.5 cm that moves during swallowing. Scanning image shows a "cold nodule" in the thyroid gland. Make the provisional diagnosis: