Familial testicular cancer is rare. It is estimated to account for 1-3% of all testicular cancers. Familial testicular cancer is currently a research priority for the National Cancer Institute's Clinical Genetics Branch (CGB). Brothers of men with a history of testicular cancer are at increased risk of testicular cancer. They are 8 to 10 times more likely to develop testicular cancer than are men who do not have a brother with testicular cancer. Men with a father who has had testicular cancer are 4 times more likely to develop testicular cancer than men who do not have a father with a history of testicular cancer.

A recently described familial testicular cancer susceptibility gene on the X- chromosome (the chromosome that men inherit from their mothers) may account for this difference in familial risk. Father to son "transmission" of cancer risk is not observed among inherited disorders caused by genes on the X-chromosome. Efforts to further refine the chromosomal location of this gene (which has been named Testicular Germ Cell Tumor-1, TGCT1) and then to determine the chemical structure of the gene are now underway. This research is being coordinated by a group of scientists known as the International Testicular Cancer Linkage Consortium.

High-risk families provide a unique opportunity to gather the epidemiological, clinical, genetic, behavioral, statistical and laboratory information necessary to define the role of susceptibility genes and other risk factors in testicular cancer development.

Testicular cancer is the most common form of cancer in young men ages 15 to 35. It accounts for about 1 percent of all cancer in men, with approximately 7,400 cases diagnosed in the United States every year. It is much more common in white males than in black males. The incidence of testicular cancer has risen over the last century, although the reason for this increase is not clear.

Risk factors for testicular cancer include undescended testicle (cryptorchidism), a prior history of cancer in one testicle (the opposite testicle is at increased risk) and family history of testicular cancer. Testicular cancer is also sometimes linked to other rare conditions in which the testes do not develop normally.

Ninety to 95% of all primary testicular cancers are germ cell (cells that form sperm) tumors, so-called "seminoma" and "nonseminoma." Seminomas make up approximately 50 percent of all testicular cancers and arise from immature germ cells. Nonseminomas arise from more mature, specialized germ cells and give rise to choriocarcinoma, embryonal carcinoma, teratoma and yolk sac tumors. An individual testicular cancer may include a mixture of cell types.

Early detection, through testicular self-exam, is particularly important because available treatments are very effective, especially in early stage tumors.