Testicular cancer is a tumorous growth that begins in the testicles and can sometimes spread to other areas of the body. It occurs when cancerous (malignant) cells develop in the tissues of a testicle. Testicular cancer is most common in men aged 20 to 35. The disease is generally successfully treatable. Testicular cancers occur in the right testicle in 52.3% of cases, and in the left testicle in 47.7% of cases.

The development of cancerous cells in both testicles can occur, but this is very rare, at a rate of approximately 2-3%.