The testicles are the two male reproductive organs that lie within the scrotum. They make sperm and testosterone, which is the male hormone predominately responsible for male sexual characteristics such as increased muscle and bone mass as well as body hair. Testis cancer starts when one of the cells within the testicle loses the ability to regulate properly and grows out of control.
The most common type of testis cancer is known as germ cell cancer. A germ cell is a portion of the testis that is responsible for making semen. The most common sign of a testis cancer is a lump or a mass within the testis.
The most common risk factor for developing testis cancer is a history of an undescended testicle. If the undescended testicle is brought down into the scrotum at a young age this risk is decreased but does not completely remove the risk. Overall, men with an undescended testicle may have up to a 5x higher risk of testis cancer, those who have surgery at an early age may only have a 2x risk.
Other risk factors for testis cancer is a family history. If you have a father or brother with testis cancer you may have an increased risk. Last, a personal history of testis cancer is a risk. Those who have been diagnosed before have a higher chance of developing testis cancer in their other testicle than the general population, however, it is still somewhat of a low risk with only 2% of people developing testicular cancer in both testes.