GPs could be routinely testing patients for their genetic risk of cancer within five years following a landmark study.
The biggest investigation of its kind ever carried out has greatly multiplied the number of known genetic markers linked to breast, prostate and ovarian cancer.
In future, the results may make it possible to single out individuals with a potentially lethal hand of genetic cards using a simple saliva test.
They can then be monitored closely for the first signs of developing cancer, or - in the most high risk cases - be offered preventative treatment.
Experts believe the cheap and easy tests could be conducted in family doctors' surgeries. Samples would initially be sent off to laboratory specialists, but eventually GPs could be doing the analysis themselves.
"We're on the verge of being able to use our knowledge of these genetic variations to develop tests that could complement breast cancer screening and take us a step closer to having an effective prostate cancer screening programme," said study author Professor Doug Easton, a Cancer Research UK scientist from Cambridge University.
Ovarian cancer tests are also envisaged, but these will take longer to develop after more research. The international scientists compared the DNA of more than 100,000 cancer patients with a similarly sized sample from the general population. They used microchip technology capable of identifying more than 200,000 genetic variants, some of which were suspected of being linked to cancer.
The analysis highlighted more than 80 inherited regions of the genetic code that increase an individual's risk of developing one of the three cancers. Each variant - a one-letter change in the code called a single nucleotide polymorphism (SNP) - on its own has a small impact on cancer risk. But added together, large numbers of the variants greatly increase the chances of disease. In the case of prostate cancer, men in the top 1% of the risk table are 4.7 times more likely than the average man to develop the disease.
Half of all men in this category who also have a strong family history of prostate cancer can expect to succumb to the illness during their lifetime.
Similarly just under a third of women in the 1% of those most at risk of breast cancer are likely to develop the disease. This excluded women carrying the well-known high risk genes BRCA1 and BRCA2. For ovarian cancer, being in the top 1% having many of the the variants more than doubled the lifetime risk from 1.8% to 4%. The variants found tended to affect the activity of genes rather than the kind of proteins they made.