Testicular cancer, or cancer of the testes, occurs in the testicles (testes), inside the scrotum. The scrotum is a loose bag of skin under the penis. Male sex hormones, testosterone, and sperm for reproduction are produced in the testicles. The testicles are a pair of male sex glands, also known as gonads. Testosterone controls the development of the reproductive organs, and other male physical characteristics.

Although testicular cancer is uncommon compared to other cancers (0.7% of all cancers), it is the most common cancer in males aged between 15 and 35 in North America and Europe. Just under 2,000 men are diagnosed with this type of cancer annually in the United Kingdom. About 70 British males die each year from testicular cancer. 8,000 American males are diagnosed and 390 die each year in the USA of this disease.

Testicular cancer occurs when the cells become malignant (cancerous) in either one or both testicles. White (Caucasian) males, especially those of Scandinavian descent are more susceptible to developing the disease compared to other men.