Benign breast conditions Quiz: Ace Your Exams

A 14-year-old boy is brought to the clinic by his mother due to progressive chest enlargement. He first noted it 1 year ago while showering in school after physical education class. Since then, it has increased in size, and he became embarrassed after being teased by his friends. He was born at term after a normal pregnancy via vaginal delivery. His development has been uneventful, and all milestones have been reached. Medical history is significant for allergic rhinitis, for which he takes fluticasone nasal spray and oral loratadine. He has had no headaches or visual changes. He does not smoke, drink alcohol or use recreational drugs. He is at the 50th percentile for height and weight; BMI is 21. Physical examination reveals bilateral firm masses extending concentrically from the nipple. The mass is more prominent on the right side. Sexual development is Tanner stage 4. The rest of the physical examination shows no abnormalities. Which of the following is the cause of this patient’s condition?