Testicular cancer is a disease in which cancer develops in one or both of the testicles. It occurs when germ cells experience abnormal growth. Germ cells, like stem cells, have the potential to form any cell in the body. Normally these cells lie dormant until sperm fertilizes an egg. If germ cells (a sexual reproductive cell) become cancerous, they multiply, forming a mass of cells called tumors that begin to invade normal tissue. When this happens these cells have the potential to form a variety of embryonic like features including but not limited to; hair, nails, teeth etc.

Testicular cancer can metastasize, meaning that it can spread to other parts of the body. During this time cells leave the original tumor from the testicle and migrate to other parts of the body through blood and lymph vessels forming new tumors. Testicular cancer spreads most often to the abdomen, liver, lungs, bones, and brain. Testicular cancer can spread rapidly and is deadly if left untreated.

Testicular cancer has a very fast onset.  If not detected early, the cancerous tumors can grow rapidly with the ability to double in size in just 10 – 30 days.

Testicular cancer is not a common cancer, but it is the most commonly diagnosed cancer after skin cancer in men aged 18–39. About 800 men are diagnosed with testicular cancer in Australia each year, accounting for about 1% of all cancers in men. It occurs most often in men aged 25–40.