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Original Article
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Volume 336:1416-1422 May 15, 1997 Number 20
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Differential Contributions of BRCA1 and BRCA2 to Early-Onset Breast Cancer
Michael Krainer, M.D., Sandra Silva-Arrieta, B.A., Michael G. FitzGerald, B.A., Akira Shimada, M.D., Chikashi Ishioka, M.D., Ryunosuke Kanamaru, M.D., Deborah J. MacDonald, R.N., M.S., Hilal Unsal, M.D., Dianne M. Finkelstein, Ph.D., Anne Bowcock, Ph.D., Kurt J. Isselbacher, M.D., and Daniel A. Haber, M.D., Ph.D.

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ABSTRACT

Background Germ-line mutations in the BRCA1 and BRCA2 genes predispose women to breast cancer. BRCA1 mutations are found in approximately 12 percent of women with breast cancer of early onset, and the specific mutation causing a deletion of adenine and guanine (185delAG), which is present in 1 percent of the Ashkenazi Jewish population, contributes to 21 percent of breast cancers among young Jewish women. The contribution of BRCA2 mutations to breast cancer of early onset is unknown.

Methods Lymphocyte specimens from 73 women with breast cancer diagnosed by the age of 32 were studied for heterozygous mutations of BRCA2 by a complementary-DNA–based protein-truncation assay, followed by automated nucleotide sequencing. In addition, specimens from 39 Jewish women with breast cancer diagnosed by the age of 40 were tested for specific mutations by an allele-specific polymerase chain reaction.

Results Definite BRCA2 mutations were found in 2 of the 73 women with early-onset breast cancer (2.7 percent; 95 percent confidence interval, 0.4 to 9.6 percent), suggesting that BRCA2 is associated with fewer cases than BRCA1 (P = 0.03). The specific BRCA2 mutation causing a deletion of thymine (6174delT), which is found in 1.3 percent of the Ashkenazi Jewish population, was observed in 1 of the 39 young Jewish women with breast cancer (2.6 percent; 95 percent confidence interval, 0.09 to 13.5 percent), indicating that it has a small role as a risk factor for early-onset breast cancer. Among young women with breast cancer, there are BRCA2 mutations that cause truncation of the extreme C terminus of the protein and that may be functionally silent, along with definite truncating mutations.

Conclusions Germ-line mutations in BRCA2 contribute to fewer cases of breast cancer among young women than do mutations in BRCA1. Carriers of BRCA2 mutations may have a smaller increase in the risk of early-onset breast cancer.


Source Information

From the Center for Cancer Risk Analysis and the Massachusetts General Hospital Cancer Center, Charlestown, Mass. (M.K., S.S.-A., M.G.F., D.J.M., H.U., K.J.I., D.A.H.); the Divisions of Biostatistics (D.M.F.) and Hematology–Oncology (D.A.H.), Massachusetts General Hospital and Harvard Medical School, Boston; the Department of Clinical Oncology, Tohoku University, Sendai, Japan (A.S., C.I., R.K.); and the Division of Pediatric Hematology–Oncology, University of Texas Southwestern Medical Center, Dallas (A.B.).

Address reprint requests to Dr. Haber at the Laboratory of Molecular Genetics, Massachusetts General Hospital Cancer Center, CNY 7, Bldg. 149, 13th St., Charlestown, MA 02129.

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