"The advantages of this study include its large sample size, inclusion of under-studied groups of women and the fact that the results are population based," said one of the study's co-authors, Robert Spirtas, Dr. P.H., former chief of NICHD's Contraception and Reproductive Health Branch and now retired.


Researchers found that 2.4 percent of the breast cancer patients had BRCA1 mutations and 2.3 percent had BRCA2 mutations. BRCA1 mutations were more common among white breast cancer patients, 2.9 percent, than among African American patients, 1.4 percent. Breast cancer patients of Jewish ancestry were also significantly more likely to have BRCA1 mutations than non-Jewish patients, 10.2 percent compared to 2.0 percent. For BRCA2, African American patients were slightly more likely to have mutations, 2.6 percent, than were white patients, 2.1 percent.


Based on their findings, the researchers went on to calculate the prevalence of BRCA1 and BRCA2 mutations in the general U.S. population. Among white and African American women ages 35 to 64, the prevalence of BRCA1 mutations is 0.06 percent and the prevalence of BRCA2 mutations is 0.4 percent, the researchers estimated.


"These findings from our large, population-based study are compatible with earlier estimates made by extrapolating from smaller studies. However, we found a slightly lower frequency of BRCA1 mutations and higher frequency of BRCA2 mutations," said the study's other lead investigator, Kathleen Malone, Ph.D., Member of the Public Health Sciences Division at the Fred Hutchinson Cancer Center. "We think the difference lies in the fact that earlier studies were confined mainly to whites, and that African American women carry BRCA2 mutations more often than white women."


The researchers also identified key predictors of whether a woman with breast cancer is likely to carry a BRCA1 or BRCA2 mutation. Such information is important because it can help to improve means of assessing which women may benefit the most from genetic testing, increased breast cancer screening and other measures aimed at early detection, treatment or prevention. The most significant predictors for BRCA1 mutations were: Jewish ancestry, a family history of ovarian cancer and a family history of breast cancer occurring before age 45.


For BRCA2 mutations, researchers uncovered fewer predictors and they had more modest effects. Among the breast cancer patients studied, the only significant predictors of a BRCA2 mutation were early age of onset (before age 45) in the patient herself or early onset of breast cancer in mother, sisters, grandmothers or aunts.

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