Testicular cancer is uncontrolled growth of abnormal cells in a testicle. This growth becomes a lump or tumor. Cells can break away from this tumor to form new growths elsewhere in the body.  The testicles are part of the male reproductive system. They are in a sac of loose skin, called the scrotum or scrotal sac, which is below the base of the penis.
 

The cause of testicular cancer is not known, but there are several risk factors. For example, men who have had an undescended testicle, even if it was surgically corrected, have a higher risk of testicular cancer. An undescended testicle is a condition in which one or both testicles did not move from inside the abdomen down into the scrotum before birth. Usually the cancer develops on the side of the undescended testicle, but sometimes the cancer is in the other side.

Some other risk factors are:

• a family history of testicular cancer
• abnormal development of the testicles, penis, or kidneys
• being HIV positive.

Testicular cancer is most common in men between the ages of 20 and 39. It is rare after the age of forty. Also, it rarely occurs in African-Americans.