Breast Cancer Test BRCA Not Always Accurate

April 5th, 2006

A widely used test for breast cancer risk failed to detect defective BRCA1 and BRCA2 genes in 12 percent of American women from high-risk families with multiple cases of breast or ovarian cancer.

The standard commercial test used in the U.S. is more accurate for women of Ashkenazi Jewish descent, a group highly susceptible to breast cancer. Myriad Genetics currently has a corner on the market for this type of the test, which can cost up to $3,000.

In the United States, only 5 to 10 percent of white women develop breast or ovarian cancers due to inherited mutations in BRCA genes. The lifetime risk for women with mutations in BRCA1 and BRCA2 genes is a staggering 80 percent for breast cancer. Young women with either of these genetic mutations are especially at risk for ovarian cancer.

They have a 40 percent or greater lifetime risk with a BRCA1 mutation and a 20 percent or higher risk if BRCA2 is involved. When these mutations are found through testing, many at-risk women opt for frequent screening or removal of their breasts and/or ovaries.

The Journal of the American Medical Association recently published results of a 2002-2005 study at the University of Washington of 300 breast cancer patients who were first in their family to be diagnosed. Researchers used a number of screening tests to identify not only BRCA genes, but also CHEK2, TP53 and PTEN — other inherited mutations that can also predict breast cancer.

The technique they used, MLPA, is a molecular way to detect genetic variations. This test is available in the U.S. to study authors only at this time. Researchers found that seventeen percent of patients had mutations previously undetected in testing, and 12 percent had “rearrangements” in the critical BRCA genes. The failure rate was higher for women who were under age 40 when first tested.

A more thorough test may be available through Myriad Genetics by the end of 2006, according to Dr. Gergory Critchfield, president of the genetic testing division of that company.

He noted that with the current test, the rate of false negatives for all women tested is less than 1 percent. The chance of missing genetic mutations in testing is generally much smaller for women who are not from very high-risk families.

Sources:  MedicineNet.com and New York Times

Entry Filed under: Breast Cancer,Breast Cancer