UK scientists have discovered a new gene linked to breast cancer.
Screening can pick up cancers
Women with a damaged copy of the gene called PALB2 have twice the risk of breast cancer, the Institute of Cancer Research scientists found.
They estimate that faulty PALB2 causes about 100 cases of breast cancer in the UK each year.
Two damaged copies of the gene also appears to cause a serious blood disorder in children, they report in Nature Genetics.
It is PALB2's job to repair mutant DNA, so people who have a faulty copy of the gene are more likely to accumulate other genetic damage too, leading to problems like cancer.
Professor Nazneen Rahman and her team studied the DNA of 923 women with breast cancer and a family history of the disease, not caused by the known breast cancer genes BRCA1 or BRCA2.
Ten of the breast cancer patients had a damaged copy of PALB2, as against none of 1,084 healthy women used as a comparison.
Carrying a faulty version of PALB2 more than doubled a woman's risk of developing breast cancer - taking her lifetime risk from one in nine to about one in five.
Although they only studied women, the scientists suspect the same gene fault may also put men at increased risk of breast cancer.
They also found children who inherited two faulty copies of PALB2 developed a sub-type of a known genetic condition called Fanconi anaemia.
This aggressive sub-type of the disease was not caused by any of the 11 genes already known to be responsible for Fanconi anaemia and was characterised by a high risk of certain cancers, including kidney and brain tumours.
Professor John Toy, of Cancer Research UK, said: "The discovery of another gene that increases breast cancer risk, albeit only for a small number of women, is very important.
"Gradually, we are beginning to learn more and more about the rogue genes that cause cancer in some families, and we hope one day to use this knowledge to help those at an increased risk of the disease."
Most breast cancers happen by chance. Only 5% are related to a known inherited breast cancer gene.