Women who have inherited a breast cancer mutation are at higher than average risk for developing breast cancer
Between 5 and 10 percent of all breast cancer cases occur in women with a genetic mutation. When a woman or man carries a genetic mutation that leads to an increased risk of breast cancer, there is a 50-50 chance the mutation will be passed on to her or his children. Whether or not the child goes on to develop breast cancer, she or he has a 50-50 chance of passing the mutation on to her or his own children.
In 1990, researchers discovered the first breast cancer gene, BRCA1, which, when mutated, increases breast cancer risk. (BR is short for breast; CA is short for cancer.) BRCA1 is a tumor-suppressor gene. When a tumor-suppressor gene is functioning normally, it can slow or stop the development of cancer. When the gene is damaged, or mutated, it doesn't work properly, and it isn't able to inhibit cancer cells. That's why women who inherit a mutation in the BRCA1 gene have an increased risk of breast cancer, and often get the disease at a young age. In 1991, researchers discovered a second gene, called BRCA2. BRCA1 mutations affect only women; BRCA2 mutations can affect both women and men.
It is estimated that about 13.2 percent of women (13 out of 100 women) in the general population will develop breast cancer in their lifetime. In contrast, it is estimated that about 36 to 85 percent of women (36 to 85 out of 100 women) who carry a BRCA1 or BRCA2 mutation will get the disease.
Women who carry a mutation in the BRCA1 or BRCA2 gene also have an increased risk of developing ovarian cancer. It is estimated that about 1.7 percent (1 to 2 out of 100) of women will develop ovarian cancer in their lifetime. In contrast, it is estimated that about 16 to 60 percent (16 to 60 out of 100) of women who carry a BRCA1 or BRCA2 mutation will develop ovarian cancer.
The BRCA gene can be mutated in 30 or 40 different ways, just as the same word can be misspelled many different ways. Shortly after the discovery of BRCA1 and BRCA2, a researcher studying Ashkenazi (Eastern European) Jews found that about 10 percent of their study population had a mutation for BRCA1. Further, there were one or two common mutations (in other words, in this group, the same one or two "misspellings" always occurred). This phenomenon, called the founder effect, occurs when a particular gene mutation appears frequently in a population because it was present in a small isolated group of "founders"—the ancestors who gave rise to most of the individuals in the present-day population. This happens frequently in populations that are geographically isolated or who tend to intermarry for religious or cultural reasons. It isn't exclusive to Ashkenazi Jews, but it does explain why Ashkenazi Jews are at higher risk of having a BRCA1 mutation.
Women with a BRCA mutation are at high risk for developing breast cancer. But having the mutation does not mean you will get breast cancer. And it does not mean that you are destined to die from breast cancer.
Learn more about risk reduction options for women with a BRCA1 or BRCA2 mutation.
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