NCI Dictionary of Cancer Terms

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The NCI Dictionary of Cancer Terms features 8,176 terms related to cancer and medicine.

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Klinefelter syndrome
(KLINE-fel-ter SIN-drome)
A genetic disorder in males caused by having one or more extra X chromosomes. Males with this disorder may have larger than normal breasts, a lack of facial and body hair, a rounded body type, and small testicles. They may learn to speak much later than other children and may have difficulty learning to read and write. Klinefelter syndrome increases the risk of developing extragonadal germ cell tumors and breast cancer.