A 17-year-old male develops a painless, firm mass beneath the nipple of his left breast. The mass is mobile, and no fluid can be expressed from the breast. The right breast is normal to examination. Which of the following conditions does this mass most likely represent?

The most common breast mass in men, especially under 25 years of age, is gynecomastia-a benign proliferation of ductal and stromal elements of the breast. It is generally an idiopathic condition, probably related to pubeal hormonal changes. Fibrocystic changes in the breast, which reflect physiological responses in the breast to cyclical levels of sex hormones, are not observed in men. Fibrocystic changes are most common in the late reproductive years and include fibrosis, cyst formation, and a variety of epithelial changes such as hyperplasia and apocrine metaplasia. Intraductal papillomas are benign neoplasms commonly evolving in the major lactiferous ducts beneath the nipple. They most commonly present with a bloody nipple discharge and are rare in men. Carcinoma of the male breast is rare, and almost always develops in the breasts of elderly men. Male breast carcinomas have a somewhat worse prognosis than their female counterpa. Grossly and microscopically they resemble ductal carcinoma in the female. Ref: Wyatt C., Kemp W.L., Moos P.J., Burns D.K., Brown T.G. (2008). Chapter 15. Pathology of the Liver, Gallbladder, and Pancreas. In C. Wyatt, W.L. Kemp, P.J. Moos, D.K. Burns, T.G. Brown (Eds), Pathology: The Big Picture.