We believe that CHK2 is involved in repairing genetic damage within a woman's breast

Dr Doug Easton

Scientists believe the discovery may eventually bring improved genetic testing for breast cancer and could lead to new ways of treating and preventing the disease.

Scientists already know that faults in the BRCA1 and BRCA2 genes greatly increase the chance of developing breast cancer - but these only account for about 2% of cases.

They believe inherited risk of breast cancer is more often caused by a combination of genes, each with a modest effect on risk.

The new study suggests that a faulty version of CHK2 is one such gene.

Vital piece

Researchers looked at how often women with breast cancer inherited a particular faulty version of the gene which has a piece missing.

They compared 1,071 breast cancer patients who had a family history of the disease, but who had not inherited BRCA1 or BRCA2, with a second group of 1,620 healthy women.

We believe that CHK2 is involved in repairing genetic damage within a woman's breast, which is why her risk of cancer goes up when the gene goes wrong.

Dr Doug Easton Cambridge University

In the patient group, 5.1% had inherited the faulty version of CHK2, compared with only 1.1% of healthy women.

In families where some members had inherited the damaged CHK2 gene, the gene was linked to cases of breast cancer more often than would be expected by chance.

Lead researcher Professor Mike Stratton, of the Institute of Cancer Research, said the research was important but much more needed to be learned about CHK2 before the information could be used in clinical practice.

Scientists also looked at inheritance of CHK2 in families with one or more cases of male breast cancer, which is far rarer than the female form and affects just 250 men each year.

The damaged gene was found in 13.5% of these cases, suggesting it substantially increases men's risk of the disease.

Interaction

The gene had no effect on risk in women who had also inherited abnormal versions of BRCA1 or BRCA2.

This suggests that it is interacting with the BRCA genes in some way and is likely to be involved in similar processes within the cell.

Scientists believe all three genes are involved in helping to repair damage that occurs to the genes within breast cells, which can lead to cancer if left uncorrected.

Researcher Dr Doug Easton, of Cambridge University, said: "We believe that CHK2 is involved in repairing genetic damage within a woman's breast, which is why her risk of cancer goes up when the gene goes wrong.

"But in women with abnormal BRCA genes, the system for repairing genes will already be faulty, so a damaged CHK2 gene cannot further increase her risk."

The research is published in the journal Nature Genetics.