(tes-TIH-kyoo-ler KAN-ser) 
Cancer that forms in tissues of one or both testicles. Testicular cancer is most common in young or middle-aged men. Most testicular cancers begin in germ cells (cells that make sperm) and are called testicular germ cell tumors.
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Figure
Anatomy of the male reproductive and urinary systems, showing the testicles, prostate, bladder, and other organs.