The bumper haul of 74 gene changes that can increase risks for the three hormone-related cancers, announced by scientists on Wednesday, is the result of the largest ever study of its kind.
It follows an international project to analyse the DNA of more than 200,000 people - half of them with cancer and half from the general population - to find alterations that are more common in individuals with the disease.
Although each gene variation increases cancer risk by only a small amount, scientists calculate that the 1 percent of men carrying lots of the alterations could have a 50% increased risk of developing prostate cancer.
Women with multiple variants could see their risk of breast cancer increase by 30%.
Doug Easton of the University of Cambridge, one of the cancer researchers who led the work, said the batch of new genetic discoveries meant medical experts would be able to develop new cancer screening programmes.
This will take time, since more research is needed to develop diagnostic tools.
"I would think that within five to 10 years this might be being used commonly, if not in a very widespread population base," said Paul Pharoah, also of the University of Cambridge.
Initially, the additional screening is likely to be targeted at patients with established cancer risk factors, such as carriers of BRCA gene faults. Women with BRCA faults are known to be at greater risk of developing breast and ovarian cancer.
Ros Eeles of Britain's Institute of Cancer Research, an expert in prostate cancer, said the new findings were the biggest leap forward yet in understanding the genetic basis of the disease.
"They allow us, for the first time, to identify men who have a very high risk of developing prostate cancer during their lifetime through inheritance of multiple risk genetic variants," she said.
In the case of prostate cancer, scientists found 23 new genetic variations - known as single nucleotide polymorphisms, or SNPs - taking the total to 78. Significantly, 16 were linked with the more aggressive forms of the disease.
For breast cancer the researchers found 49 new SNPs, more than doubling the number previously identified, and in ovarian cancer the tally was 11.
A few of the variations were common to more than one cancer type, suggesting there may be common mechanisms of action that could be targeted by new drugs.
Developing medicines using the insight gained by the latest research will take many years, even assuming that drugmakers can produce compounds that work effectively. Encouragingly, though, companies such as Roche, the market leader in cancer, are getting better at making drugs that apply biochemical "brakes" to tumour cells.
The scientists stressed that genes, while important, were just one side of a complex mix of factors leading to cancer.
"Lifestyle and environmental risks act in concert with the genetics. It is not one or the other - it is always both together," Pharoah told reporters.
The new research was published in a series of papers in Nature Genetics, Nature Communications, PLOS Genetics, the American Journal of Human Genetics and Human Molecular Genetics.