TORONTO — An international team of researchers, including several from British Columbia, has discovered a new gene for breast and ovarian cancer they believe may be a missing link between hereditary and sporadic forms of breast cancer.

If the findings hold true in further studies, they may help doctors determine at an early stage which women have a highly virulent form of cancer so they can tailor treatment accordingly.

"We see these mutations in breast cancers that have a particularly aggressive behaviour," said Dr. David Huntsman, a genetic pathologist with the British Columbia Cancer Agency.

"And these are breast cancers which, since they're node negative breast cancers, we would have thought they would have been less aggressive tumours."

The findings were published Wednesday in Cell, one of the most prestigious international scientific journals.

"Dancing on the tables occurred when we heard it got into Cell," Huntsman admitted in an interview from Vancouver on Tuesday.

The team, led by researchers at Cambridge University, has shed light on a conundrum which has puzzled breast cancer researchers for some time involving the activity of a gene known to cause some hereditary breast cancers.

BRCA 1 and BRCA 2 are genes which help restore damaged DNA before it can become cancerous in normal breast tissue. But women who carry a mutated form of these genes run a high risk of developing breast and ovarian cancer.

Breast cancers attributable to these mutations make up only a small portion - less than five per cent - of all breast cancer cases. The rest are sporadic cases which occur in women without strong family histories of the disease.

Researchers haven't been able to figure out why the BRCA genes aren't implicated in the development of sporadic breast cancer - why they behave normally in 95 per cent of women with breast cancer but not in the other five per cent.

While trying to puzzle that out, the British teams discovered a new gene, which they dubbed EMSY. The gene, which produces a protein of the same name, interacts with BRCA 2.

With the help of scientists at the BC Cancer Agency and Vancouver Coastal Health Research Institute, the researchers determined that in some sporadic cancers the problem isn't BRCA 2, it's EMSY.

"What they've discovered - and we've determined the clinical relevance of their discovery - is that instead of having abnormalities in BRCA 2 itself, it's its partner gene EMSY which is abnormal in the cancers," Huntsman said.

By studying hundreds of tissue samples from the cancer agency's breast cancer archive, they saw that in 13 per cent of sporadic breast cancers, EMSY ran amok. For some unknown reason, the gene reproduced itself many more times than it should have, creating too much of its protein.

Examination of the clinical files of the women showed these cancers were very aggressive; women with extra copies of the EMSY gene survived an average of 6.4 years, compared with 14 years for women with normal EMSY levels.

The difference was particularly striking in women whose cancers had been caught before they moved into the lymph nodes. Such early detection is generally thought to improve survival chances but not so with the women who had the mutated EMSY gene.

"Discovering such an important new gene is very exciting and gives us a piece in the jigsaw we've been looking for," Prof. Tony Kouzarides, leader of the Cambridge team, said in a statement.

"It's going to give us new lines of investigation and potentially exciting angles of attack."

Huntsman said future research will look at whether this type of breast cancer responds better to some forms of existing chemotherapies than others. As well, the researchers are hoping they may be able to figure out how to turn off the mutated EMSY gene in these types of tumours.

"If we could develop a drug that would work really well for 13 per cent of breast cancer women, and use a test so that we could just target those 13 per cent of women and offer just those women the drug, we will have made a huge difference," he said.

But he cautioned it will be some time before research can be translated into changes in treatment.

"This is a tantalizing lead which may be a useful test for the laboratory, but a lot of work has to be done before it's ready for prime time."