NEW YORK (Reuters Health) - An international team of researchers reported on Monday that they have discovered a new breast cancer gene that is believed to be associated with 1% of all female breast cancer cases and 9% of all male breast cancer cases.

The mutation in the gene, known as CHEK2, confers a twofold increase in breast cancer risk in women, who typically have about a 13% chance of developing cancer in their lifetime. The gene mutation carries a tenfold increase of a man's risk of breast cancer, a much rarer occurrence.

In contrast, the known breast cancer genes BRCA1 and BRCA2 are "riskier" in terms of developing cancer. About 50% to 60% of women with those genes develop cancer by age 70.

"We have suspected that 'low risk' cancer genes exist but they have been difficult to prove with certainty," said Dr. Nazneen Rahman of the Institute of Cancer Research in Surrey, UK, in an interview with Reuters Health. "(The CHEK2 discovery) is the first to be proved to a high degree of certainty," Rahman added.

In the investigation, the researchers found that the CHEK2 mutations were found in 5.1% of 1,071 breast cancer patients without a mutation in the BRCA1 or BRCA2 genes, according to the report published in the April 21st issue of the journal Nature Genetics.

However, only 1.1% of 1,620 healthy people were found to have the gene variation.

The CHEK2 gene is located on human chromosome 22, according to Rahman, and it plays a role in the repair of damaged DNA.

"DNA damage can cause cancer and thus if the function of CHEK2 in repairing DNA is reduced then the likelihood of cancer can occur," Rahman told Reuters Health.

The researchers believe that CHEK2 acts in concert with another, as yet unidentified gene, to cause breast cancer.

The new discovery adds to a small but growing body of research about the role genes play in breast cancer.

Currently, experts know that a family history of breast cancer is one of the strongest risk factors for breast cancer, especially among young women. Nearly half of women with early-onset breast cancer have a family history of breast or ovarian cancer, yet only 9% of these women have a BRCA1 or BRCA2 mutation, suggesting that other genetic factors may play a role.

Although early-onset breast cancer has a strong genetic link, scientists report that they have yet to discover the genes responsible for the disease in most patients.

With regard to the implications for breast cancer treatment and or prevention, Rahman emphasized caution in interpreting the results.

"One percent of the population carries this mutation, but only a minority will go on to develop breast cancer--therefore it is unclear at this stage whether people with the mutation would benefit from any different management."

He added, "In the long-term, this finding informs us about the biological pathways and genes that are involved in breast cancer and this information is helpful in developing new treatments."

SOURCE: Nature Genetics 2002;DOI:10.1038/ng879.

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