BRCA Mutations Don't Raise Breast Cancer Risk Equally

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This study focused on the 181 women who were shown to be mutation carriers.

First-degree relatives of BRCA1 and 2 carriers had a higher risk of developing breast cancer if their proband (the relative whose breast cancer diagnosis first brought the family history to light) was diagnosed at a younger age (35 or under). The overall study only looked at women who had been diagnosed under the age of 55.

There was also a non-statistically significant trend toward higher risk for first-degree relatives of women with contralateral breast cancer as opposed to unilateral breast cancer.

The results strongly indicate that factors other than the BRCA mutations influence risk.

"If everyone with a mutation has exactly the same risk, then the presence of the mutation is the only factor that influences risk in carriers, [and] there are no other factors that can influence risk," Begg explained. "The fact that we see that age at diagnosis in the proband influences risk in the relatives implies that there is something else about the carrier families with a "young" proband that must influence risk. The presumption is that these families are passing on other genetic characteristics that positively influence breast cancer risk."

Although the authors state there is no need for wide screening of women yet, future technological advances may make such screening feasible.

"Lots of research is being done on the whole genome to identify new risk factors for breast cancer, and there's a certain amount of debate as to whether this is a worthwhile exercise or not. There's only a point to searching if something is to be found there," Begg explained. "This kind of study suggests that there is something to be found, and that it is worthwhile doing these studies not just on mutation carriers but on people with breast cancer on the whole. Our premise is that the additional breast cancer risk factors that will be found will be applicable to carriers just like to anyone else."

"This is a very, very interesting article, and very important. These two genes represent about 7 percent of all breast cancers and usually account for breast cancer in families and in young women," said Dr. Jay Brooks, chairman of hematology/oncology at Ochsner Health System in Baton Rouge, La. "We're understanding more about how patients can accept the risk that has been assigned to them. This is a very important paper going forward."

More information

There's an overview of the genetics of breast cancer at the U.S. National Cancer Institute.