Prostate cancer is rare in men under 50 years old. However, the risk increases steadily with age. By the time they are 80, more than half of all men will have some cancerous growth, though in most cases it goes unnoticed. Prostate cancer is usually slow-growing and, in men who have it, is often not the cause of death.
The causes of prostate cancer are largely unknown. It is clear that the chances of developing prostate cancer increase in men over 50. Close relatives of men who have had prostate cancer are also more likely to be affected. Ethnic origin appears to play a part: men of African heritage seem to be at highest risk, and men of Far Eastern descent the lowest.
It may be possible to reduce the risk by avoiding a high fat diet through, for example, cutting down on dairy foods and red meat.
Prostate cancer seems to run in some families, suggesting an inherited or genetic factor. Having a father or brother with prostate cancer doubles a man's risk of developing this disease. The risk is even higher for men with several affected relatives, particularly if their relatives were young at the time of diagnosis. Scientists have identified several inherited genes that seem to increase prostate cancer risk, but they probably account for only a small fraction of cases. Genetic testing for these genes is not yet available.
Some inherited genes increase risk for more than one type of cancer. For example, inherited mutations of the BRCA1 or BRCA2 genes are the reason that breast and ovarian cancers are much more common in some families. The presence of these gene mutations also increases prostate cancer risk. But they are responsible for a very small percentage of prostate cancer cases.
The most consistent risk factors associated with prostate cancer are age, family history and African-American ethnicity. Hormonal factors, as well as high levels of animal fat and red meat in the diet, are also suspected risk factors.
Several occupational studies have linked farming to prostate cancer risk. However, the variety of environmental exposures in the farming community such as pesticides, engine exhausts, solvents, dusts, animal viruses, fertilizers, fuels, and specific microbes, have made it difficult for researchers in previous studies to sort out which of these factors is linked to specific diseases.
Exposure to certain agricultural pesticides may be associated with an increased risk of prostate cancer among pesticide applicators, according to a large recent study known as the AHS (Agricultural Health Study) looking at the causes of cancer and other diseases in the farming community. The AHS is a collaborative effort involving the National Cancer Institute (NCI), the National Institute of Environmental Health Sciences, and the Environmental Protection Agency.
There is also a weak association between prostate cancer and cadmium exposure, associated with the occupational environments of mining and newspaper printing.
Some studies have raised questions about a possible relationship between vasectomy (an operation to cut or tie off the two tubes that carry sperm out of the testicles) and the risk of developing cancer, particularly prostate and testicular cancer. Such a relationship, if proven, would be of importance, as about one in six men over the age of 35 in the United States has had a vasectomy.