There are five known genetic risk factors for prostate cancer. Each is associated with a higher than normal chance of developing the disease. The news from a new study is that their effect is cumulative — meaning that a man's chances of getting prostate cancer are dramatically higher, the more of these risk factors he has inherited. Because these risk factors can be detected with a simple blood test, men will soon have a quick and inexpensive way to get an accurate idea of their chances of developing prostate cancer. Those who know they are at greater risk can, with their doctors, be more vigilant and more aggressive in diagnosing prostate cancer in its earlier, more treatable stages.

Researchers at Wake Forest University School of Medicine and their colleagues found that a man with four of the five genetic factors has a risk 400 to 500 percent higher than that of a man with none. They then added a family history of prostate cancer to make six risk factors. A man with at least five of the six factors had increased risk of more than 900 percent.

Their results are published in the online and February 25, 2008 issue of the New England Journal of Medicine.

The scientists say that these five genetic variants, plus family history, explained almost half of all prostate cancer cases. The study analyzed DNA samples from 2,893 men with prostate cancer and 1,781 healthy individuals of similar ages, all in Sweden.

"This is significant and could affect clinical care," said senior researcher Jianfeng Xu, M.D., Dr. PH., professor of epidemiology and cancer biology. "The information could substantially improve physicians' ability to assess risk and determine the need for more aggressive screening or even a biopsy."

The study is one of the first to show that a combination of different genes can affect cancer risk. Other teams are busy searching for combinations of genes that may be implicated in common diseases such as diabetes and asthma.

Currently, age, race and family history are the three factors (in addition to genetic variants) thought to be associated with increased risk of prostate cancer. Family history is believed to account for about 10 percent of prostate cancer cases, compared to the 40 percent of cases accounted for by the five genetic factors.

"Our finding provides an opportunity to supplement the well-established risk factors by looking at how many of these variants a man has inherited," said Xu. "It may provide a much better weapon to guide clinicians."