In 1942, Dr. Harry Klinefelter and his coworkers at the Massachusetts General Hospital in Boston published a report about nine men who had enlarged breasts, sparse facial and body hair, small testes, and an inability to produce sperm. Reserachers later discovered that men with this condition, which was eventually termed Klinefelter's syndrome, had an extra X chromosome and an XXY combination of sex chromosomes instead of the usual XY combination in males.
XXY boys do not progress normally through puberty. Their testes remain child-sized and therefore do not produce enough of the male hormone, testosterone. As adolescents, XXY boys are taller than average and may lack facial hair.
About one-third of XXY boys will develop enlarged breasts, a condition known as gynecomastia. This condition is different than just fat accumulation giving the appearance of having breasts. Gynecomastia is true breast development.
Men with Klinefelter's syndrome and enlarged breasts have the same risk of breast cancer as women do. Therefore, XXY males are 20 to 50 times more likely than the average male to develop breast cancer. Unlike women, however, XXY males are more likely to develop cancer in both breasts or unusual second types of cancer.
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