Scientists say they have found two genetic mutations which could triple the risk of developing bowel cancer.
Bowel cancer can be cured with early treatment
Earlier this year, a study funded by Cancer Research UK found the first section of the human genome linked to bowel cancer.
Now the team has found another two mutations within that which could raise the overall risk two to three-fold.
Writing in the journal Nature Genetics, they say they could cause a third of all cases - about 12,000 per year.
Around 36,000 new diagnoses in the UK each year
Third most common cancer after breast and lung
Causes almost 16,100 deaths in the UK every year
Two-thirds of cases are in the large bowel (colon), rest in the back passage (rectum)
80% of cases are in people who are 60 years of older
Earlier, the researchers found a part of the genome which is responsible for causing Hereditary Mixed Polyposis Syndrome (HMPS) - a condition which significantly increases bowel cancer risk in Jews of Ashkenazi descent.
They then went back to look again more closely at that region.
But instead of pinpointing genes specifically relevant to Ashkenazi Jews, they made a discovery with much wider implications.
They found that the HMPS region also had two faults which are present in many more cases of bowel cancer in the general population.
Professor Ian Tomlinson, joint lead researcher at the Institute of Cancer Research said he was "delighted" at the discovery.
"Finding out that a region we thought was only relevant to bowel cancer risk in Ashkenazi Jews was also related to risk in the wider UK population is very important," Prof Tomlinson said.
"This could help us understand how different variants of the same gene affect risk and how genes interact to increase overall risk."
Dr Lesley Walker, director of cancer information at Cancer Research UK, said that in the past, scientists had focused on high risk genes - those which caused a particular cancer in many generations of the same family, often to devastating effect.
"Most of those high risk genes have now been discovered," Dr Walker said.
"So the emphasis has moved to genes which do carry a risk, but a lower one - genes which are much more common in the population."
On their own, the two newly found mutations present too small a risk to warrant the development of a screening test.
But scientists hope that in the future it may be possible to develop a test for a combination of mutations like them which on mass would more significantly increase the risk of bowel cancer.
The discovery is the latest to emerge from an effort by Cancer Research UK to search the entire human genome for mutations linked to cancer.
The charity also has plans to investigate the possible genetic causes of lung and ovarian cancer.
Ashkenazi Jews are descendants of Jews from Germany, Poland, Austria and Eastern Europe.