The study reviewed here suggests that women who have a family member with an abnormal breast cancer gene but don't have an abnormal gene themselves do NOT have higher-than-average breast cancer risk. These results were reported at the 2008 San Antonio Breast Cancer Symposium.
Most inherited cases of breast cancer are associated with two abnormal genes: BRCA1 (BReast CAncer gene 1) and BRCA2 (BReast CAncer gene 2). Women with an abnormal BRCA1 or BRCA2 gene have up to an 85% risk of developing breast cancer by age 70. Their risk of ovarian cancer is also increased. Abnormal BRCA1 and BRCA2 genes are found in 5% to 10% of all breast cancer cases in the United States. Other research has found that a woman's breast cancer risk may be higher than average when one or more of her close relatives has an abnormal BRCA1 or BRCA2 gene, even if she doesn't have an abnormal gene herself. The study reviewed here suggests that this may not be accurate.
Researchers followed the medical histories of almost 400 women from 28 families in which someone had an abnormal BRCA1 or BRCA2 gene. All the women in the study had been tested for an abnormal breast cancer gene before joining the study and none of them had an abnormal gene. Even though none of the women had an abnormal breast cancer gene, 13% of them chose to have their ovaries removed (prophylactic oophorectomy) to reduce breast cancer risk. It's likely that the women opted for ovary removal because they and their doctors thought their breast cancer risk was much higher than average, based on family history. Removing the ovaries can reduce breast cancer risk in high-risk women by dramatically lowering estrogen levels in the body. Estrogen can promote the growth of some breast cancers.
When the researchers analyzed the 18 years of medical information from the women in the study, they found that the women's breast cancer risk was the same as the average woman's, even after taking into account that some of the women in the study had their ovaries removed. In other words, women who don't have an abnormal breast cancer gene seem to have an average risk of breast cancer, even if someone else in their family does have an abnormal breast cancer gene.
While the women in this study were followed for 18 years, they were all young (about 31) when they joined the study. It could turn out that their breast cancer risk will be higher later on, after even more follow up time.
If you have a family member that has tested positive for an abnormal breast cancer gene, it's important to consider getting tested yourself. Just because one of your relatives has an abnormal gene doesn't mean you do, too. If you decided to get tested, work with your doctor to assess your breast cancer risk after you get your test results. Talk to your doctor about whether a genetic counselor could help you better understand your risk. Base your health decisions on the best information available to you.
For more information on genetics and breast cancer, visit the Breastcancer.org Genetics and Breast Cancer Risk section.
SAN ANTONIO, Dec. 16 (MedPage Today) -- Women from BRCA1/2 mutation-positive families do not have an increased risk of breast cancer if they are not mutation carriers, data from a large cohort study suggest.
Mutation-negative women from mutation-positive families had a breast cancer risk similar to that of women in the general population, Larissa A. Korde, M.D., of the National Cancer Institute, reported at the San Antonio Breast Cancer Symposium.
The findings countered those from other recent studies suggesting as much as a fivefold increase risk of breast cancer in mutation-negative women from BRCA1/2-positive families.
"There still needs to be more data to make good recommendations for this group," said Dr. Korde. "It shows that the jury is still out. We don't know what is driving risk, other than the BRCA mutation in these families."
Women who are carriers of BRCA1/2 mutations have a 40% to 85% lifetime risk of breast cancer. Recent studies have suggested that women from mutation-carrying families have an increased risk of beast cancer even if they do not have the mutations, said Dr. Korde.
Seeking to validate or refute those results, the investigators compared data from an NCI cohort of mutation-positive families with data on age- and race-matched women included in the NCI Surveillance, Epidemiology and End Results 9 Cancer Registry.
They mailed questionnaires to women from mutation-positive families, and 395 mutation-negative women from 28 mutation-positive families responded.
Eligibility criteria for the analysis included at least a third-degree relation to a known mutation carrier, cancer status confirmed by the respondent or a family member, and tested or inferred negativity for BRCA1/2 mutations.
Women in the study cohort enrolled at an average age of 31.3 and had been followed for an average of 17.7 years.
Nine cases of breast cancer were documented in the study cohort during follow-up, whereas 12 cases would have been expected. The findings translated into an unadjusted breast cancer odds ratio of 0.75.
Dr. Korde reported that 50 women (13%) in the study group had prophylactic bilateral oophorectomy. In analyses that adjusted for the risk reduction conferred by oophorectomy, the mutation-negative women had fewer or no more than the expected number of breast cancers.
"It's a relatively young-aged cohort, and with more years of follow-up, these numbers could clearly change," said Dr. Korde.
"Even with a large sample size and 7,000 person-years of follow-up, we had very few cases. Although this is probably one of the largest studies looking at this issue, it's still small in comparison to what would need to be done to definitively answer the question."
Dr. Korde reported no potential conflicts of interest.
Primary source: San Antonio Breast Cancer Symposium Source reference: Korde LA, et al "Breast cancer risk in mutation-negative members of known BRCA1/2 mutation-positive families" SABCS 2008 Abstracts. 132s. Abstract 1093.
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