Also called testicular cancer; a malignant tumor that begins in the testicle, one of the two organs located in the protective pouch between the legs of a boy or man. The testicles produce sperm cells and secrete the principal hormones (including testosterone) that control male sexuality and physical characteristics, such as facial hair, a deeper voice, and enlargement of the penis at puberty. Testicular cancer is rare, but it is the most common malignancy in men between 18 and 34 years old. The dis¬ ease is highly curable, particularly when detected and treated early.