Women who carry a BRCA mutation are typically told that they have a 60 to 80 percent risk of developing breast cancer by age 70. A study in this weekâ€™s Journal of the American Medical Association suggests that this figure might be incorrect, and that women with a BRCA mutation are actually more likely to have a 36 to 52 percent risk of developing breast cancer by age 70.
Why the discrepancy? Researchers derived the 60-80 percent statistic from studies of families known to carry a BRCA mutation. (Often these were families who chose to be studied.) The new study was a population-based, case-control study that compared women who developed a second breast cancer in the opposite breast with women who had cancer in only one breast. The researchers began by looking at 2000 women with breast cancer. Within this group, there were 1394 women who had had breast cancer in one breast. Of these women, 73 (5.2%) had a BRCA mutation. There were also 704 women who had developed breast cancer in both breasts. In this group, 108(15.3%) carried a BRCA mutation.
The researchers then looked at breast cancer rates in all of these womenâ€™s first-degree relatives: their mothers, sisters, and daughters. This analysis revealed that although having a first-degree relative increased risk, the risk levels were not the same. Specifically, the researchers found that relatives of carriers who were diagnosed at age 35 or younger had a 52 percent chance of being diagnosed with breast cancer by age 70 and a 95 percent chance by age 80. In contrast, relatives of carriers who were diagnosed at age 45 or older had a 36 percent chance of being diagnosed with breast cancer by age 70 and a 44 percent chance by age 80.
This suggests, as the researchers point out in their article, that among BRCA carriers there are â€œadditional unknown risk factors for breast cancer, which are more prevalent in the families of women diagnosed at a younger age, and in the families of women with contralateral breast cancer.â€ Finding out what these risk factors are will help us fine-tune risk estimates even further. It might also lead to new ways of preventing or treating breast cancer in these BRCA carriers.
Iâ€™ve always tried to stress that being high risk is not the same as being being destined to get the disease. It’s also clear that different women handle this high risk in different ways. Some choose to undergo more frequent screening with mammography and MRI to try to catch a cancer as early possible while others choose to reduce their risk by having their breasts and/or ovaries removed.
Will learning that their risk is 36 to 52 percent instead of 60 to 80 percent lead some women to change what risk-reduction options they choose? Perhaps. But there will also be some women who says that this news reinforces the decision they have made to have more frequent screening. And there will be others who say that while the risk might be lower, it is still way too high for them to not choose prophylactic mastectomy and oophorectomy.
Bottom-line: It will remain a personal decision whether a woman chooses to learn if she carries a BRCA mutation and, if she is tested, how she responds to the knowledge that she does.