Genes determine cancer risk
Scientists have discovered a gene which may trigger spontaneous cases of breast and ovarian cancer.
People who inherit faulty BRCA genes are at increased risk of developing either form of cancer
But the new gene, EMSY, appears to shut down a form of fully-functioning BRCA - increasing risk in those not normally thought to be vulnerable.
The research, by Cambridge University for Cancer Research UK, will be published in the journal Cell.
Scientists hope it will lead to new tests to predict the development of both breast and ovarian cancer.
Lead researcher Professor Tony Kouzarides, said: "Discovering such an important new gene is very exciting and gives us the piece in the jigsaw we've been looking for.
"We'll now have a much more sophisticated image of the genetic changes triggering breast and ovarian cancer in women who haven't inherited a high risk of cancer, but develop it anyway.
"It's going to give us new lines of investigation and potentially exciting angles of attack."
Inheriting faulty BRCA genes gives women a high risk of breast and ovarian cancer - but only 5% of breast cancers run in families like this.
Scientists have been hunting for the genes that cause sporadic breast cancers - the other 95% of cases - ever since the BRCA genes were discovered, eight years ago.
They had long suspected BRCA2 might play a role in sporadic breast and ovarian cancers - despite the fact that the gene is very rarely damaged within these tumours.
Professor Kouzarides' team found EMSY has a role in turning genes on and off and in repairing damaged DNA.
It is particularly effective at switching off BRCA2.
Tests on hundreds of tumour samples revealed that 13% of breast cancers, and 17% of ovarian cancers contained extra copies of the gene.
However, it was never found in normal tissue - and hardly ever in other types of tumour.
Professor Carlos Caldas, who also worked on the study, said: "We've always thought factors that are important in inherited breast cancers should also be playing a role in other kinds and it's heartening to know that we hadn't been barking up the wrong tree.
"It should help us in the development of new, targeted treatments against breast and ovarian cancer, particularly as cancers with high levels of the new gene seem to behave in a similar way to inherited forms.
"EMSY could also form the basis for new types of predictive test."
EMSY seems to play a particularly important role in aggressive forms of breast cancer.
Women whose tumours had extra copies of the EMSY gene survived for 6.4 years on average, compared with 14 years for those whose breast cancers had normal amounts of EMSY.
The difference in survival was particularly great among women who at diagnosis had not suffered any spread of the cancer to their lymph nodes.
This suggests it might be possible to test for EMSY early on in a woman's course of treatment, in order to predict how aggressive their disease is likely to become.