In future, genetic variant results may make it possible to single out high-risk individuals using a simple saliva test.
They can then be monitored closely for the first signs of developing cancer or 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.
The chip used in the analysis cost just £30, and although the study relied on blood samples the same tests can easily be carried out on saliva.
Professor Douglas Easton said there was a "big excitement" about discovering around 80 genetic variants linked to common cancers.
"We can use this information to develop risk profiles of individuals to identify people who are at either high or low risk of these cancers," he added.
People at high risk would be encouraged to have earlier and more regular screenings for the disease, he said.
Everyone's genetic code is made up of 3 billion letters - a Cs, Gs, Ts or As.
All those codes contain mistakes. Most of them are harmless, but what these researchers have done is to look for the ones that aren't.
Scientists did that by cracking the codes of 100,000 people with either breast cancer, prostate cancer or ovarian cancer.
They found 80 of those mistakes that put people at high risk of getting cancer.
They say that a test for those mistakes could be available in GPs surgeries soon.
If you find out you've got one of those genetic alterations, it doesn't mean you will get cancer, just that you are at high risk. But that might convince you to, for example, cut down on drinking or smoking or to go for more regular screenings.
Revolutionary tests for the most common forms of cancer could soon be available thanks to a large study which revealed links between genetic variations and breast, prostate and ovarian cancers.
University of Cambridge scientists tested 200,000 people to discover the genetic alterations most common in people who had cancer.
Professor Ros Eeles, professor of oncogenetics at The Institute of Cancer Research (ICR), said: “These results are the single biggest leap forward in finding the genetic causes of prostate cancer yet made.
"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."
Research by Cambridge scientists could lead to routine tests for patients genetic risk of cancer within five years.
The study 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.
More than 1,000 scientists from 130 institutions in Europe and the US took part in the Collaborative Oncological Gene-environment Study (Cogs).
– Professor Doug Easton - Cancer Research UK
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
Dr Harpal Kumar, chief executive of Cancer Research UK, which co-funded the research, said:
This groundbreaking international work highlights how complex cancer is.
Hundreds, if not thousands of genes are likely to play a role in how cancers start.
But by understanding why some people seem to be at greater risk of developing cancer we can look towards an era where we can identify them and take steps to reduce their chances of getting cancer or pick up the disease at its earliest stages."