The etiology of gynecomastia is unknown. There seems to be no increased inc
idence of malignancies in patients with idiopathic gynecomastia; however, p
atients with Klinefelter syndrome exhibit an increased incidence of maligna
ncy. The authors reviewed the results of 34 patients with gynecomastia diag
nosed in adolescence who, following initial evaluation, had a mastectomy. T
he estrogen and progesterone receptors were analyzed in these patients. Thr
ee of the patients were diagnosed with Klinefelter syndrome. These three pa
tients exhibited elevated amounts of estrogen and progesterone receptors. N
one of the patients who were not diagnosed with this syndrome demonstrated
significant elevation of their estrogen or progesterone receptors. The pres
ence of elevated estrogen and progesterone receptors in patients with Kline
felter 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 wh
y these patients' disease rarely degenerates into malignancy.