3/21/2006

Commercial genetic testing does not detect all cancer-associated mutations

Despite a negative (normal) genetic test for mutations in the BRCA1 and BRCA2 genes, about 12 percent of breast cancer patients from high-risk families carried previously undetected cancer-associated mutations, according to a study in the March 22/29 issue of JAMA, a theme issue on women's health.

Inherited mutations in BRCA1 and BRCA2 predispose to high risks of breast and ovarian cancer. Lifetime risks of breast cancer are as high as 80 percent among U.S. women with mutations in these genes, according to background information in the article. Risks for young women with inherited BRCA1 or BRCA2 mutations are particularly increased. Among white women in the U.S., 5 percent to 10 percent of breast cancer cases are due to inherited mutations in BRCA1 and BRCA2. Inherited mutations in other genes, including CHEK2, TP53 and PTEN, can also influence risk of breast cancer.

"The clinical dilemma is what to offer to women with a high probability of carrying a mutation in BRCA1 or BRCA2 but with negative commercial test results. Technically, the answer is at hand. The mutations identified in our study that were missed by commercial testing are detectable using other approaches that are currently available," the researchers write. They add that for families testing negative (wild type) for BRCA1 and BRCA2 by conventional sequencing, multiplex ligation-dependent probe amplification (MLPA - a molecular method to detect genetic variation) followed by sequence confirmation of breakpoints in patients' genomic DNA is the current best choice for evaluating the wide range of genomic rearrangements in BRCA1 and BRCA2. Clinical testing using MLPA is currently not available in the U.S.

"As more breast cancer susceptibility genes of different penetrances are identified, clinicians will be increasingly challenged to offer the most appropriate genetic tests, to assist patients in interpreting the results, and to optimize risk reduction strategies," the authors conclude. "Effective methods for identifying these mutations should be made available to women at high risk."

US commercial genetic testing does not detect all cancer-associated mutations in certain genes

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