Breast Cancer Gene Tests Incomplete?

U.S. Test Works Fine but Doesn't Check for All Mutations, Researcher Says

Medically Reviewed by Louise Chang, MD on March 21, 2006
From the WebMD Archives

March 21, 2006 -- Researchers are calling for more thorough tests for gene mutations that raise the risk of breast and ovarian cancer.

"This is not a criticism of the competence of commercial testing," Mary-Claire King, PhD, said in a media teleconference. However, she says current U.S. genetic testing doesn't cover all of the thousands of cancer-related mutations that can occur on the BRCA 1 and BRCA 2 genes.

Such mutations can dramatically raise the risk of breast cancer or ovarian cancer, says King, who works in Seattle at the University of Washington's medical school.

King and colleagues studied 300 people with breast cancer or ovarian cancer who had a strong family history of those diseases. Twelve percent of those patients had BRCA 1 or BRCA 2 gene mutations that were undetected on a standard gene test, the researchers report.

Their study appears in The Journal of the American Medical Association.

High Stakes

Women with a strong family history of breast or ovarian cancer often use genetic testing in weighing preventive treatments including surgery to remove their ovaries or breasts, King notes.

"Obviously, those are horrifically invasive procedures, and they are not procedures that one would undertake unless one had an extremely high risk of breast cancer and of ovarian cancer, such as are conferred by the cancer-associated mutations of these genes," King says.

King's study included 300 people with breast cancer or ovarian cancer who had at least four cases in the family of either disease. Almost all of the breast cancer patients were women.

All participants had gotten commercial gene tests that came back with normal results. Those tests were correct, King's team found. "They got it right," King says.

However, those tests clearly state that they don't cover all genetic mutations that might affect cancer risk. "They're perfectly straightforward about that," King says.

Thousands of Mutations

"There are thousands of mutations in BRCA 1 and BRCA 2, and that's why looking for them bird by bird is not going to work," King says.

She and her colleagues did follow-up testing on genetic material from participants' blood. They found that 12% of the group had cancer-related BRCA 1 or BRCA 2 gene mutations.

The standard test should still be done first, King says. "It's important, it's necessary, but it's not sufficient," she says. The follow-up tests used in her study aren't currently available in the U.S.

When asked what women should do in light of her findings, King says, "I don't honestly know." She says creating better tests "is not easy, technically, but it is doable," and that she and other researchers continue to look for other genes that affect cancer risk.

Show Sources

SOURCES: Walsh, T. The Journal of the American Medical Association, March 22/29, 2006; vol 295: pp 1379-1388. Mary-Claire King, PhD, University of Washington School of Medicine, Seattle. News release, JAMA/Archives.
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