testicular cancer.Testicular cancer is a disease in which malignant (cancer) cells form in the tissues of one or both testicles.Anatomy of the male reproductive and urinary systems, showing the testicles, prostate, bladder, and other organs.Anatomy of the male reproductive and urinary systems, showing the testicles, prostate, bladder, and other organs.The testicles are 2 egg-shaped glands inside t