Review Question - QID 210489

A 65-year-old man presents to his primary care physician with a neck mass. He first noticed a firm mass on the anterior aspect of his neck approximately 4 months ago. The mass is painless and has not increased in size since then. He has also noticed occasional fatigue and has gained 10 pounds in the past 4 months despite no change in his diet or exercise frequency. His past medical history is notable for gout for which he takes allopurinol. He denies any prior thyroid disorder. He runs 4 times per week and eats a balanced diet of mostly fruits and vegetables. He does not smoke and drinks a glass of wine with dinner. His family history is notable for medullary thyroid cancer in his maternal uncle. His temperature is 97.8°F (36.6°C), blood pressure is 127/72 mmHg, pulse is 87/min, and respirations are 19/min. On exam, he has a firm, symmetric, and stone-firm thyroid. A biopsy of this patient's lesion would most likely demonstrate which of the following findings?