BRCA mutations not associated with colorectal cancer risk, studies suggest

12/29/03

Two studies in the January 7 issue of the Journal of the National Cancer Institute suggest that mutations in the genes BRCA1 and BRCA2 are not associated with an increased risk of colorectal cancer.

Mutations in BRCA1 and BRCA2, which are present in about 2.5% of the Ashkenazi Jewish population, have been associated with an increased risk of breast and ovarian cancer, but it is unclear whether these mutations also increase the risk of colorectal cancer. Some studies have suggested an increased risk of colorectal cancer among mutation carriers, whereas other studies have found no such association. Current nationally recognized guidelines recommend that all BRCA1/2 mutation carriers be informed that they may be at an increased risk for colorectal cancer.

Tomas Kirchhoff, Ph.D., Kenneth Offit, M.D., and their colleagues at the Memorial Sloan-Kettering Cancer Center in New York compared the incidence of BRCA1/2 mutations in 586 Ashkenazi Jewish patients with colorectal cancer with that of 5,012 patients without a known history of colorectal cancer. The authors found no association between the presence of a BRCA mutation and risk of colorectal cancer.

In a second study, Bethany L. Niell and Stephen B. Gruber, M.D., Ph.D., of the University of Michigan, Ann Arbor, and their colleagues performed genetic testing on 1,422 patients with colorectal cancer and 1,566 control subjects without colorectal cancer in a population-based study in Israel. They also found no association between the presence of a BRCA mutation and the risk of colorectal cancer.

A family history of breast cancer in a female relative was not associated with an increased risk of colorectal cancer, even after adjusting for the presence of a BRCA founder mutation. The authors conclude that Ashkenazi BRCA founder mutations do not confer a strongly elevated risk of colorectal cancer. Similarly, a family history of breast cancer does not appear to be a strong risk factor for colorectal cancer in this population.

In an accompanying editorial, Judy E. Garber, M.D., and Sapna Syngal, M.D., of the Dana-Farber Cancer Institute and Brigham and Women's Hospital, Boston, ask, "These studies were certainly well done, but are they the final words on the subject? It depends on the exact question one is trying to answer." They note that a future study may find an increased risk of colorectal cancer among BRCA1/2 mutation carriers, but the current studies indicate that it will be a small increase at most, or limited to a particular subset of mutation carriers. "Intensified targeted colorectal cancer screening and prevention should be directed only to the subset of BRCA mutation carriers who have remarkable personal or family colorectal cancer history or other risk factors."

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