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Gene boosts breast cancer risk



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A specific gene mutation may be a marker for raised breast cancer risk in women with a family history of the disease, researchers report.

Family members of women who have had cancer in both breasts and who carry a damaged version of the CHEK2 gene are at a greatly increased risk of developing breast cancer, according to a new study.

"This gene might have a use as a screening tool for other family members," says Dr. Jay Brooks, chairman of hematology/oncology at the Ochsner Clinic Foundation in Baton Rouge, La.

Brooks was not involved with the study, which appears in the Oct. 29 issue of The Lancet.

The data also suggest that CHEK2 might interact with other, currently unknown genes to increase risk.

The discovery of the CHEK2 gene was first announced in a paper in 2002, notes Lesley Walker, director of cancer information at Cancer Research U.K., which helped sponsor the study.

In 2004, another paper assessed the risk and found that women with the damaged version of CHEK2 faced double the chance of developing breast cancer, compared with women with normal versions of the gene. Even a doubling of absolute risk is considered fairly low, however.

Two better-known breast cancer-linked genes, BRCA1 and BRCA2, confer a much greater risk, experts point out.

According to the National Cancer Institute, women with an altered BRCA1 or BRCA2 gene are three to seven times more likely to develop breast cancer.

Experts believe that family histories of breast cancer not accounted for by BRCA 1 or 2 can be explained by the existence of groups of genes that may each confer a low risk, but work together to increase the odds for malignancy.

Experts believe CHEK2 may be responsible for 1 to 2 percent of all breast cancers. But the question has always been: Which 1 to 2 percent?

"Scientists have been casting around trying to decide who should be tested for CHEK2, and that's been difficult because it's a relatively low risk in the general population, and it's a rare gene," Walker says. "People are still thinking: When should we test for CHEK2?"

The authors of this paper wanted to determine the risk of breast cancer in relatives of women who had the damaged CHEK2 gene and a history of cancer in both breasts, called bilateral breast cancer.

To that end, they tested 469 women with bilateral breast cancer for this specific CHEK2 variant. They then looked at the incidence of breast cancer, prostate cancer and other cancers in all first-degree relatives of women with or without the variant.

First-degree relatives of women who had had bilateral breast cancer and a normal version of CHEK2 were at a cumulative breast cancer risk of 23.8 percent by the age of 80, or about triple the normal risk of 7.9 percent, the researchers reported. The male relatives were also at twice the risk of prostate cancer, although this finding needs to be confirmed in other research, the scientists says.

Relatives of women with bilateral breast cancer and the damaged CHEK2 gene were at a cumulative risk of 58.8 percent by age 80, or more than seven times the normal risk. It appeared that they were at a higher risk of prostate cancer, as well.

Given that the CHEK2 gene only occurs in 2 percent or less of the population, it doesn't make sense to test everybody for the variant, the researchers say.

But testing for CHEK2 in women with a specific family history of breast cancer -- illness involving bilateral breast cancer in a first-degree relative -- might make sense, the authors stated.

These families may also be key to finding other low-risk genes that affect susceptibility to breast cancer.

"Those families could help us find other low-risk genes or moderate-risk genes that could be important," Walker says.

(The HealthDay Web site is at http://www.HealthDay.com.)

c.2005 HealthDay News

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