Scientists have long known that women with a gene called BRCA1 have an increased risk for breast and ovarian cancer, but it's far from the only gene influencing that risk. Now, five newly discovered genetic markers may help researchers refine risk estimates for not only women with BRCA1, but others as well.

The markers were found by studying the genes of thousands of women who have BRCA1 and breast cancer, and comparing them to the genes of women who have BRCA1 but had not developed breast cancer.

The findings are published in the October issue of the journal Nature Genetics.

Women with certain BRCA1 mutations have about a 65 percent lifetime risk of getting breast cancer, said study author Fergus Couch, a researcher at the Mayo Clinic in Rochester, Minn. The average woman in the United States has a 12 percent risk. However, these risk estimates are based on population data and not catered to the individual, Couch said.

"The problem is that we've never been able to figure out what an individual's risk is," Couch said. "Everything is just given a population number and the individual has no clue where they stand."

Any woman's risk might be closer to 30 percent or 90 percent, depending on her genes, Couch said. By finding more genetic markers for breast cancer, researchers might help women who have the BRCA1 gene who are trying to decide whether to take preventative action and have their breasts removed, Couch said. An increasing number of women are having mastectomies as a preventative measure or as a treatment for breast cancer, according to a 2009 study in the Journal of Clinical Oncology.

Genetic markers

Couch and his colleagues — from 20 different institutions in 11 different countries — examined the genes of 1,193 women under age 40 who had the BRCA1 gene and who also had breast cancer, and compared them with the genes of 1,190 women under age 35 who had the BRCA1 gene but did not have breast cancer.

They found 96 genetic spots where the two groups differed. The spots are called single nucleotide polymorphisms, or SNPs.

Next, they looked for these 96 SNPs in a larger population. By comparing the genes of about 3,000 women who have the BRCA1 gene and breast cancer with the genes of 3,000 women with the gene who did not have cancer, they narrowed the field to five SNPs that were more strongly were associated with breast cancer risk. These five are located in a region of chromosome 19.

These markers were also linked to an increased risk of breast cancer in women without the BRCA1 gene. In these women, the markers were associated with particularly aggressive breast cancers that do not respond well to treatment.

Future work

More research needs to be done to figure out the mechanisms by which these markers might contribute to the development of breast cancer.

The researchers hope to identify more markers to better refine their estimates of a woman's breast cancer risk, Couch said.

"We're going to need constellations of these types of things. This is really the first one, and we need a bunch more to really do it properly," he told MyHealthNewsDaily.

In three or four more years, they could have a set of markers that could be useful to patients, he said.

The study was funded by the Breast Cancer Research Foundation, Susan G. Komen for the Cure, the National Institutes of Health, and Cancer Research UK.

This article was provided by MyHealthNewsDaily, a sister site to LiveScience.