Q. A 35-year-old man presents to his primary care physician with a six-month history of weight loss and fatigue. He reports that he has been feeling more tired than usual and has lost 10 pounds without any changes in his diet or physical activity. He also reports a family history of thyroid carcinoma, which was diagnosed in his mother when she was 40 years old. The patient's vital signs on presentation are: blood pressure 170/96 mm Hg, pulse rate 80 bpm, and respiratory rate 16 bpm. The physical examination reveals a thin patient with a palpable mass in the lower neck. Further evaluation reveals elevated serum levels of calcium, calcitonin, parathyroid hormone and carcinoembryonic antigen and an ultrasound of the neck shows a solid mass in the lower pole of the thyroid. The patient undergoes a total thyroidectomy, and the pathology report confirms medullary thyroid carcinoma. Genetic testing reveals a RET proto-oncogene mutation. Further evaluation reveals a pheochromocytoma and parathyroid adenoma. What is the most likely diagnosis for this patient?