Testicular cancer begins in the cells of the testicles (testes). A little smaller than golf balls, the testicles are located within a sac of skin called the scrotum, which lies beneath the base of the penis.
As part of the male reproductive system, the testicles produce sperm as well as the male hormone called testosterone.
More than 90 percent of testicular cancers develop in the cells that produce sperm called germ cells.
Germ Cell Tumors
There are two main types of germ cell tumors (GCTs): seminomas and non-seminomas. Tumors that are a mix of both of these germ cells are treated as non-seminomas because they grow and spread like them.
Developing from the sperm-producing germ cells of the testicle, seminomas are split into two main subtypes:
- Classical (Typical) Seminomas: More than 95 percent of seminomas are classical and usually occur in men between 25 and 45 years of age.
- Spermatocytic Seminomas: Although rare, this type of seminoma usually occurs in older men around the age of 65; grows slowly; and is less likely to spread compared to classical seminomas.
Seminomas can increase blood levels of a protein of called human chorionic gonadotropin (HCG), which can be detected by a blood test. Measuring levels of this tumor marker in the blood can help in diagnosis and treatment.
This type of germ cell tumor usually occurs in men in their late teens to early 30s. There are four main types of non-seminoma tumors (most non-seminoma tumors are a mix of at least two of the following types):
- Embryonal Carcinomas: Present in about 40 percent of testicular tumors, the cells of embryonal carcinomas resemble the tissue of very early embryos, when viewed under a microscope. These carcinomas tend to grow rapidly; spread outside the testicle; and increase blood levels of a tumor marker protein called alpha-fetoprotein (AFP), as well as HCG.
- Yolk Sac Carcinomas (Yolk Sac Tumor, Endodermal Sinus Tumor, Infantile Embryonal Carcinoma or Orchidoblastoma): When seen under a microscope, the cells of these cancerous tumors look like the yolk sac of an early human embryo. Yolk sac carcinomas are the most common form of testicular cancer in children and usually increase blood levels of AFP.
- Choriocarcinomas: Occurring in adults, this type of cancer tends to be rare but aggressive, often spreading rapidly to distant organs of the body and increasing the blood levels of HCG.
- Teratomas: Teratomas are germ cell tumors with cells that, when seen under the microscope, resemble one of the three layers of a developing embryo. There are three main types of teratomas:
- Mature teratomas are generally benign and rarely spread to nearby tissues and distant parts of the body.
- Immature teratomas are likely to grow into surrounding tissues and to spread (metastasize) outside the testicle.
- Teratomas with malignant transformation are very rare cancers.
Carcinoma in Situ (Intratubular Germ Cell Neoplasia)
Carcinoma in situ (CIS) is a noninvasive form of germ cell cancer that can slowly progress to invasive cancer and spread to other parts of the body.
Because CIS causes no symptoms, the only way to diagnose it is to perform a biopsy: remove a small tissue sample and examine it under a microscope.
Tumors can also develop in the stroma: the supportive and hormone-producing tissues of the testicles. These gonadal stromal tumors make up less than 5 percent of adult testicular tumors but up to 20 percent of childhood testicular tumors. There are two main types:
- Leydig Cell Tumors: These tumors are usually benign and form in the Leydig cells, which produce male sex hormones. Leydig cell tumors do not usually spread beyond the testicles.
- Sertoli Cell Tumors: Sertoli cell tumors are usually benign and begin in the Sertoli cells, which support and nourish the sperm-producing germ cells.