Signs and symptoms of testicular cancer include:

• A lump or enlargement in either testicle
• A feeling of heaviness in the scrotum
• A dull ache in the abdomen or groin
• A sudden collection of fluid in the scrotum
• Pain or discomfort in a testicle or the scrotum
• Enlargement or tenderness of the breasts
• Back pain

Cancer usually affects only one testicle.

It's not clear what causes testicular cancer in most cases.

Doctors know that testicular cancer occurs when healthy cells in a testicle become altered. Healthy cells grow and divide in an orderly way to keep your body functioning normally. But sometimes some cells develop abnormalities, causing this growth to get out of control — these cancer cells continue dividing even when new cells aren't needed. The accumulating cells form a mass in the testicle.

Nearly all testicular cancers begin in the germ cells — the cells in the testicles that produce immature sperm. What causes germ cells to become abnormal and develop into cancer isn't known.

Factors that may increase your risk of testicular cancer include:

• An undescended testicle (cryptorchidism). The testes form in the abdominal area during fetal development and usually descend into the scrotum before birth. Men who have a testicle that never descended are at greater risk of testicular cancer than are men whose testicles descended normally. The risk remains elevated even if the testicle has been surgically relocated to the scrotum.

Still, the majority of men who develop testicular cancer don't have a history of undescended testicles.

• Abnormal testicle development. Conditions that cause testicles to develop abnormally, such as Klinefelter syndrome, may increase your risk of testicular cancer.
• Family history. If family members have had testicular cancer, you may have an increased risk.
• Age. Testicular cancer affects teens and younger men, particularly those between ages 15 and 35. However, it can occur at any age.
• Race. Testicular cancer is more common in white men than in black men.