Women who inherit mutations in one of two genes involved in inherited breast cancer have an 82 per cent lifetime risk of developing the disease, according to a new study carried out by the New York Breast Cancer Study Group (NYBCS). They found that women who have a genetic mutation, but no relatives affected by breast or ovarian cancer, have exactly the same risk as women with a mutation and a family history of the illnesses. 'The risks are high, full stop' says lead researcher Mary-Claire King, of the University of Washington in Seattle. The study, published in Science, also showed that women in the study born after 1940 tended to develop the disease earlier than those born before 1940, but that a healthy lifestyle could delay the onset of the disease.
Most breast and ovarian cancers are not inherited, but around 5-10 per cent are caused by inherited mutations - many of them in one of two genes, called BRCA1 and BRCA2. Previous studies of families with several affected members have shown that the lifetime risk for women who inherit a mutated BRCA1 or BRCA2 gene can be as high as 85 per cent. Such women also have an increased lifetime risk of ovarian cancer: 40-65 per cent for those with a BRCA1 mutation, and 20 per cent for those with a BRCA2 mutation. The new study shows that these risks are the same for all women who inherit BRCA1 or BRCA2 mutations - regardless of whether they have any affected relatives or not. 'Mutations in BRCA1 and BRCA2 are inherited from fathers as often as from mothers, although fathers are rarely affected by breast cancer. So if a family is small, there may be no warning a mutation is present' said King. An article commenting on the study suggested that it might be time to consider looking for BRCA1 and BRCA2 mutations in the general population, to identify women at high risk of breast and ovarian cancer. These women could then be offered preventative treatments, such as increased breast screening.
The NYBCS team studied a group of 1008 Ashkenazi Jewish women who had developed breast cancer, regardless of whether or not they had a family history of the illness. They identified 104 that had inherited a mutated BRCA1/2 gene, and then tested all the family members of these women, to find out who else had inherited the same mutation. Their results showed that by 80 years of age, all women carrying a BRCA1/2 mutation have an 82 per cent risk of developing breast cancer, and a 54 or 23 per cent risk of ovarian cancer (for BRCA1 and BRCA2 carriers respectively). They also found that those born before 1940 had a 24 per cent chance of developing breast cancer by the age of 50, whereas those born after 1940 had a 67 per cent chance. King thinks that this difference could be partly down to a less healthy modern lifestyle. 'As a group we are more sedentary and we weigh more, but that is not the whole explanation and I don't know what is' she said. But the researchers also found that the disease appeared later in women who exercised and were slim in their teens, and in those who had children. 'It was a surprise, but a source of hope to learn that factors over which we have some control made a difference in the age at which these highest-risk women developed breast cancer' said King.