The testicles, or testes, are the male sex glands that produce sperm. Because they also manufacture the male sex hormone testosterone, the testicles are also considered part of the endocrine system.
Reproductive cells called germ cells develop into sperm through a process of cellular division called meiosis. Under normal circumstances, cell division is regulated. Sometimes the germ cells begin to divide uncontrollably and, instead of producing functional sperm, the germ cells create copies of themselves. When this happens, the cells are considered cancerous. This kind of out-of-control division may happen in other types of cells in the testicles, but nearly 95 percent of all testicular cancers develop in germ cells.
About 9,610 new cases of testicular cancer are expected to be diagnosed in the United States in 2020, according to the American Cancer Society.
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