For women who carry genetic mutations linked to breast cancer, a new study provides grim confirmation that their risk is high and that younger women with the genes are more likely to develop the disease at an early age than were previous generations of carriers.
The findings apply to only a small portion of breast cancer patients: those who have mutations in the genes BRCA1 or BRCA2, which account for just 5 percent to 10 percent of new cases a year, which number about 200,000. The mutations also increase a woman's risk of ovarian cancer.
The new study provides compelling evidence that every woman with a BRCA mutation is at high risk, even those from families with few cases of cancer or those who inherited the gene from their fathers. Some doctors had thought carriers in those two groups might be in less danger than others, but that is not the case. Half the women in the study who had BRCA mutations and breast cancer had no family history of breast cancer.
"I hate to be the bearer of bad news, but I'd rather be the bearer of bad news to young women in a way that will allow them to save their lives," said Dr. Mary-Claire King, a geneticist at the University of Washington and the senior author of the study, which is being published today in the journal Science. "Women need to know what they're up against."
Mutation carriers who exercise regularly and avoid obesity as teen-agers develop breast cancer later in life than those who are inactive or heavy, King said.
"You can't make the risk go away, but a healthy lifestyle does ameliorate it to some degree," King said.
Dr. Barbara Weber, a breast cancer expert at the University of Pennsylvania who was not part of the study, said it made an important contribution by proving that all carriers were at high risk. She said some carriers had been told, erroneously, that they had little to worry about.
Women are not routinely tested for the gene mutations, partly because the test is expensive and complicated. They are usually advised to discuss testing with their doctors if they develop breast cancer at a young age or have relatives who had breast or ovarian cancer when they were young.
The study, which involved patients and their families at a dozen cancer centers in and around New York City, found that by age 80, a woman with a mutation in either BRCA gene had an 82 percent chance of developing breast cancer. By contrast, the average woman's risk at 80 is about 13 percent.
The BRCA mutations greatly increase a woman's risk of ovarian cancer as well: For BRCA1 it is 54 percent, and for BRCA2, 23 percent, compared with an average risk of only about 2 percent.
The study also found striking increases in risk in younger women with the mutations: Carriers born after 1940 had a 67 percent risk of developing breast cancer by age 50, compared with a risk of only 24 percent at age 50 among carriers born before 1940. The reason for that is not clear.