There is a broad variation in the risk of developing breast cancer among people who carry the BRCA1 and BRCA2 gene mutation, according to a study published in the Journal of the American Medical Association.

BRCA1 and BRCA2 are gene mutations that predispose carriers to breast cancer. The magnitude of the risk of breast cancer in BRCA1 and BRCA2 carriers is critical for guiding decisions concerning cancer prevention options. The risk of breast cancer in BRCA1 and BRCA2 mutation carriers has been examined in many studies, but relatively little attention has been paid to the degree to which the risk may vary among carriers, according to background information in the article.

Colin B. Begg, Ph.D., of Memorial Sloan-Kettering Cancer Center, New York, and colleagues conducted an investigation to determine the extent to which risks of BRCA1 and BRCA2 carriers vary with respect to observable and unobservable characteristics. Participants in the Women's Environmental Cancer and Radiation Epidemiology (WECARE) Study, who were previously diagnosed with unilateral breast cancer (affecting only one side) or contralateral breast cancer (affecting the opposite side of an initial breast cancer), were genotyped for mutations in BRCA1 and BRCA2. All participants had their initial breast cancer diagnosed during the period from January 1985 through December 2000, before the age of 55.

"Among the 1,394 participants with unilateral breast cancer, 73 (5.2 percent) were identified as carriers of deleterious mutations (42 with BRCA1 and 31 with BRCA2)," the authors report. "Among the 704 participants with contralateral breast cancer, 108 (15.3 percent) were identified as carriers of deleterious mutations (67 with BRCA1 and 41 with BRCA2)."