KEY POINTS:
The first genetic test that allows young men to assess their risk of developing prostate cancer in later life could be available as early as next year, scientists said yesterday.
Several teams of researchers have identified seven genetic risk factors that account for about half of prostate cancers
in the general population.
The scientists believe the findings could form the basis of a DNA test that could be used to identify young men at higher-than-average risk who could then be screened more closely for early signs of prostate cancer as they reach middle age.
Although 60 per cent of cases of prostate cancer occur in men over 70, there are also strong genetic factors, with the risk increasing in men whose fathers developed the disease.
Much of the research focus in recent years has been on a region of chromosome 8 - one of the 23 pairs of human chromosomes - which appears to be instrumental in conferring a high risk of inheriting a predisposition to prostate cancer.
"There is a fairly large genetic component to the risk. That means you don't inherit the disease, you inherit various dispositions to the disease," said Kari Stefansson, the head of the Icelandic company deCode Genetics which formed part of the research team.
"We have found two sets of genetic variants on chromosome 8 that have dramatic impacts on the risk of prostate cancer," Dr Stefansson said.
"When you can identify the risk, there is a theoretical possibility of developing it into a pre-diagnostic test to screen men. It would be a reasonable goal to turn it into a genetic test before the end of this year or the beginning of the next," he said.
Three teams of scientists, who published their findings in the journal Nature Genetics, have identified seven genetic risk factors in total on two regions of chromosome 8.
"The study has identified combinations of genetic variants that predict more than a five-fold range of risk for prostate cancer," said David Reich, an assistant professor of genetics at Harvard Medical School.
"I think the genetic variations are clearly predictive of prostate cancer risk, but it is not clear whether the medical community is ready because of the ethical issues," he said.
One issue concerns the accuracy of the non-genetic, antigen test for prostate cancer, and whether it is advisable to carry out surgery on what may turn out to be a relatively benign tumour.
The scientists found that the high-risk and the low-risk variants of the genetic combinations are common within the general population but in some ethnic groups, notably Afro-American men, the high-risk combinations are far more common, Dr Reich said.
One high-risk variant of the genetic factors for instance is found in only 2 to 4 per cent of men in the general population but in about 42 per cent of African-American males.
"The identification of these genetic variants is an important step in helping us to understand the higher risk for prostate cancer in African Americans compared with other US populations and ... why some men develop prostate cancer and others do not," said Christopher Haiman of the University of Southern California in San Diego.
The researchers studied the DNA of thousands of men with prostate cancer from ethnic groups from America, Japan and Europe.
The scientists said the region of chromosome 8 implicated in prostate cancer does not contain any known genes, which may indicate an as-yet undiscovered genetic trigger for cancer.
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