Genes
Some genes appear to increase a man’s risk of developing many different types of cancer, including prostate cancer and testicular cancer.
Prostate Cancer
Genes have been linked to prostate cancer, especially in those men who were diagnosed with prostate cancer at a relatively young age (younger than 55 years old). The younger the person is when he is diagnosed, the higher the risk is for male relatives to have prostate cancer at a young age. Prostate cancer seems to run in some families, suggesting an inherited or genetic factor. Having a father or brother who has prostate cancer almost doubles a man’s risk of developing this disease. The risk is even higher for men who have several affected relatives, particularly if their relatives were young at the time of diagnosis.
The causes of prostate cancer are still poorly understood, and reflect complex interactions between genetic and environmental factors. Still, genes are clearly important, because a man whose father and grandfather had prostate cancer is two to three times more likely to have the disease than a man with no such family history. The ethnic and family contributions to the probability of developing prostate cancer reveal that there is a strong genetic basis for this disease, as there is for most cancers.
Scientists have identified several inherited genes that seem to increase prostate cancer risk, although the genes probably account for only a small fraction of cases.
Some inherited genes increase the risk for more than one type of cancer. For example, inherited mutations of the BRCA1 or BRCA2 gene cause a higher risk of breast and ovarian cancers in women who inherit them. A man who inherits one of these gene mutations also has a higher prostate cancer risk; however, the mutations are responsible for a very small percentage of prostate cancer cases.
The genetics of inherited prostate cancer are complex, and family linkage studies suggest that mutations in at least six different genes may be involved. So far, scientists have identified a few genes that appear to be responsible for a man’s inherited tendency to have prostate cancer:
• HPC1 (hereditary prostate cancer gene 1)
• HPC2 (also known as ELAC2)
• HPCX (found on the X chromosome)
• CAPB (named because of its connection to cancers of the prostate and brain)
Research on these genes is still preliminary, and genetic tests are not yet available.
Most gene mutations related to prostate cancer develop during a man’s life rather than before birth. Every time a cell prepares to divide into two new cells, it must make a copy of its DNA. This process is not perfect, and sometimes errors occur. Fortunately, cells have repair enzymes that correct mistakes in the DNA. But some errors may slip past (especially if the cells are growing rapidly), leaving the DNA in the new cell with a mutation. Exposure to radiation or cancer-causing chemicals may cause DNA mutations in many organs of the body, but these factors have not been proved to be important causes of mutations in prostate cells.
Further studies of these genes could help shed light on the biological features of prostate cancer, which may provide suggestions for developing new treatments. Men who have a family history of prostate cancer who are concerned about an inherited risk for this disease should talk with their doctor, who may suggest consulting a health professional trained in genetics. Much more work is needed, however, before scientists can say exactly how changes in these genes are related to prostate cancer.
Testicular Cancer
HIWI, discovered at Duke University Medical Center in 2002, is the first gene known to be linked to testicular cancer. The Duke research shows that 63 percent of men who inherit the overactive form of the hiwi gene could develop seminoma.
Testicular cancers are grouped into two main classes: seminoma and nonseminoma. Nonsemino-mas tend to be more aggressive than seminomas and in most cases quickly spread to the lymph nodes.
Although hiwi is the first gene known to be highly correlated to seminoma, scientists are close to identifying other genes suspected of playing a role in other testicular cancers. Cancer researchers in the United Kingdom announced in February 2000 they had located (but not yet identified) a gene on a region of chromosome X associated with testicular cancer. The gene, TGCT1, can increase a men’s risk of testicular cancer by up to 50 times. Other researchers have located testicular cancer susceptibility on chromosome 19 in mice.