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Cancer starts when cells in the body begin to grow out of control. Cells in nearly any part of the body can become cancer, and can spread to other areas of the body. To learn more about how cancers start and spread, see What Is Cancer?

Testicular cancer can start in one or both testicles. It is most often found in young men but can occur at any age.

The testicles

The testicles (or testes) are part of the male reproductive system. In adult men, each one is normally a little smaller than a golf ball. They are held in a sac of skin called the scrotum. The scrotum hangs beneath the base of the penis.

The testicles have 2 main functions:

  • They make the male hormones such as testosterone.
  • They make sperm, the male cells that combine with a female egg cell to start a pregnancy.

Testicles are made of several kinds of cells, each of which can develop into one or more types of testicular cancer. Each type of cancer is treated differently, so it is important to know which kind you have.

Main types of testicular cancers

Germ cell tumors

More than 9 out of 10 cancers of the testicles start in the germ cells. As used here, the term “germ” means seed. Germ cell tumors start in the cells that make sperm.

There are 2 main types of germ cell tumors in men (seminomas and non-seminomas), which occur about equally:

Seminomas: These tumors tend to grow and spread more slowly than most other testicular cancers. There are different types of seminomas. They usually develop in men between 25 and 45.

Non-seminomas: These tumors tend to develop earlier in life than seminomas. They are often found in men between their late teens and early 30s. There are 4 main types of non-seminomas:

  • Embryonal carcinoma
  • Yolk sac carcinoma
  • Choriocarcinoma
  • Teratoma

Most tumors are a mix of 2 or more of these different types. But all non-seminoma cancers are treated the same way.

Mixed germ cell tumors: These cancers have both seminoma and non-seminoma cells. They are treated as non-seminomas because they grow and spread like non-seminomas.

Carcinoma in situ of the testicle: Testicular germ cell cancers may begin as a non-invasive form of the disease called carcinoma in situ (CIS) or intratubular germ cell neoplasia. This is sometimes found when a man has a biopsy of the testicle because of infertility. It may also be found when a man has a testicle removed because it didn’t descend into the scrotum completely (called cryptorchidism).

In CIS, the cells don’t look normal under the microscope, but they have not yet spread beyond the seminiferous tubules (where sperm cells are formed). Carcinoma in situ may not always go on to become invasive cancer.

Experts don’t agree about the best treatment for CIS. Since CIS doesn’t always become an invasive cancer, many doctors feel that observation (watching and waiting) is the best course of action.

Stromal tumors

These tumors start in the cells that make hormones and in the supportive tissues (the stroma) of the testicles. They make up less than 1 in 20 adult testicular tumors but up to 1 in 5 testicular tumors in boys. The 2 main types of stromal tumors are:

  • Leydig cell tumors
  • Sertoli cell tumors

Stromal cell tumors are often benign (not cancer). They usually do not spread beyond the testicle and can be cured by surgery. But a few stromal cell tumors spread to other parts of the body (metastasize). These cancers do not respond well to chemotherapy or radiation treatment.

Secondary testicular tumors

Tumors start in another organ and then spread to the testicle are called secondary testicular tumors. These are not true testicular cancers – they are named and treated based on where they started.

A number of cancers can spread to the testicle, but the most common cancers are lymphomas and acute leukemias.

Last Medical Review: 01/20/2015
Last Revised: 02/12/2016