Although the exact cause of testicular cancer has not been identified, several predisposing factors seem to increase risk. These include a past medical history of undescended testicle(s), abnormal testicular development, Klinefelter's syndrome (a sex chromosome disorder that may be characterized by low levels of male hormones, sterility, breast enlargement, and small testes), or previous testicular cancer.

Other factors are under investigation as possible causes, such as exposure to certain chemicals and infection with the human immunodeficiency virus (HIV). A family history of testicular cancer may increase risk. There is no link between vasectomy (an operation to cause sterility) and elevated risk of testicular cancer.

Between 6,000 and 8,000 men will be diagnosed with testicular cancers each year. Although testicular cancer accounts for 1% of all cancers in men, it is the most common form of cancer in young men 15 to 40 years old. It may also occur in young boys, but only about 3% of all testicular cancer is found in this group. White American men have about five times the risk of African-American men and more than twice the risk of Asian-American men. The risk for testicular cancer has doubled among white Americans in the past 40 years but has remained the same for African-Americans. The reasons for these differences are not known.

Types of Testicular cancer

• Seminomas account for about 30 - 40% of all testicular tumors. These are usually is found in men in their 30s and 40s. The condition is usually localized to the testes, although in about 25% of cases it has spread to lymph nodes.
• Non-seminomas account for 60% of all testicular tumors; subcategories of these tumors are listed below. Non-seminoma tumors often contain more than one of the following cell types:
  • Embryonal carcinoma (about 20% of testicular cancers) occurs in 20-30 year olds and is highly malignant. It grows rapidly and spreads to the lung and liver.
  • Yolk sac tumor (about 60% of all testicular cancers in young boys).
  • Teratomata (about 7% of testicular cancers in adult men and 40% in young boys).
  • Choriocarcinoma (rare).

Stromal cell tumors are a kind of tumor that is made of Leydig cells, Sertoli cells and granulose cells. These tumors account for only 3-4% of all testicular tumors. However, these do make up nearly 20% of all childhood testicular tumors. These tumors may secrete a hormone -- estradiol -- that can cause one of the symptoms of testicular cancer, gynecomastia (excessive development of male breast tissue).