A genetic test would look for several breast cancer genes
A simple test for gene faults which increase the risk of breast cancer is getting nearer, UK scientists suggest.
If given to all women at the age of 30, those found to be at highest risk could be regularly screened for signs of disease, they say.
The article, in the New England Journal of Medicine, suggests older "low risk" women might need less breast screening.
But screening younger women could increase the number of expensive MRI scans needed.
Scientists know that breast cancer risk is determined partly by a woman's inherited genetic makeup, and partly by other factors, such as lifestyle.
By testing people with a strong family history of the disease, they have gradually uncovered which genes appear to be contributing to that risk.
The best known of these are faults in the BRCA1 and BRCA2 genes, but there are several others.
Researchers say that it is becoming feasible to work out whether a woman is at "low", "moderate" or "high" risk of cancer by looking at which combinations of these she has.
A woman at "low risk" might be offered the chance to defer the start of conventional breast screening on the NHS, which starts at age 50, while someone at high risk might be screened every year from 30.
Dr Paul Pharoah, from the University of Cambridge, who is funded by the charity Cancer Research UK, said: "We are a few years away from a new and powerful range of genetic tests for breast cancer.
"We believe genetic testing has the potential to enable doctors to identify a woman at an increased risk of breast cancer who would benefit from mammography at an early age or woman who may benefit from regular MRI scanning as well.
"This approach would also identify a 55-year-old woman with a low chance of breast cancer who possibly wouldn't need such regular checks."
He said the test would be simple - a swab rubbed inside the mouth - and cheap.
However, the arrival of universal gene testing could present a challenge to the current NHS breast screening programme.
While there is evidence that conventional X-ray mammography is effective at saving lives in women over 50, there is little evidence that it can help younger women.
This is because the density of breast tissue is different before the menopause, making it harder for cancers to be spotted.
The National Institute for Clinical Excellence recommends the use of MRI scans in younger women at high risk of breast cancer, but this could be far more financially draining if used widely.
Professor Bruce Ponder, who led the research, said: "We expect such technology to develop very fast in the next decade so it's important that we start thinking about how best to apply these advances."
A spokesman for MacMillan Cancer Support said that older women should be encouraged to attend breast screening, regardless of any risk revealed by a future gene test.
"At Macmillan we would strongly urge women not to defer screening.
"It is a free facility that can save lives and all women should be encouraged to take it up when offered to them."
A spokeswoman for charity Breakthrough Breast Cancer said improvements on conventional mammography, such as new "digital" mammography, might be increasingly important.
But the NHS Breast Screening Programme said such gene testing was still a long-way off.