The etiology of gynecomastia is unknown. There seems to be no increased incidence of malignancies in patients with idiopathic gynecomastia; however, patients with Klinefelter syndrome exhibit an increased incidence of malignancy. The authors reviewed the results of 34 patients with gynecomastia diagnosed in adolescence who, following initial evaluation, had a mastectomy. The estrogen and progesterone receptors were analyzed in these patients. Three of the patients were diagnosed with Klinefelter syndrome. These three patients exhibited elevated amounts of estrogen and progesterone receptors. None of the patients who were not diagnosed with this syndrome demonstrated significant elevation of their estrogen or progesterone receptors. The presence of elevated estrogen and progesterone receptors in patients with Klinefelter syndrome provides a potential mechanism by which these patients may develop breast neoplasms. The absence of elevated estrogen and progesterone receptors in patients with idiopathic gynecomastia may serve to clarify why these patients' disease rarely degenerates into malignancy.
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