Testicular cancer is a disease in which cancerous cells form in the tissues of one or both testicles. Though it is the most common cancer in men between the ages of 15 and 35, testicular cancer is relatively rare and almost always curable if detected early.

Testicular cancer can develop in one or both testicles, and more than 90% of testicular cancer develops in the cells that make sperm, known as germ cells.