It found that more than 80% of women who tested positive for the harmful mutations ultimately chose to have surgery to remove their ovaries, breasts or both.
"Almost all of the women who screened positive did take some sort of action," said lead researcher Dr Marc D. Schwartz, of the Lombardi Comprehensive Cancer Center in Washington, DC.
That may not seem surprising. But Schwartz said there has been some scepticism about how many women with BRCA mutations would choose to have their ovaries or breasts removed.
"It's a difficult decision to have prophylactic (preventive) surgery," Schwartz noted. "There's been a perception that risk-reducing surgery, especially risk-reducing mastectomy, was not something most mutation carriers would choose."
But most studies on the issue, at least in the US, have been short-term – looking at women's choices in the year or so after a BRCA test result. Women in the current study were followed for an average of just over five years.
Risk women are exposed to
Defects in the BRCA1 and BRCA2 genes substantially raise a woman's lifetime risks of breast and ovarian cancers – to a roughly 60% chance of developing breast cancer, and a 15 to 40% risk of ovarian cancer.
By comparison, the average US woman has a 12% chance of developing breast cancer during her lifetime and only a 1.4% chance of ovarian cancer.
Because of the high risks, experts recommend that some women with a strong family history of breast or ovarian cancers be screened for the gene mutations.
For women who test positive, it's a "pretty firm recommendation" that they have their ovaries removed by about age 40, Schwartz said.
That's because ovarian cancer is difficult to catch early and, therefore, has a high death rate. And studies have found that when a woman has a BRCA mutation, surgery to remove the ovaries not only slashes her risk of developing the cancer by about 90%, but can also extend her life.
The recommendations on preventive mastectomy are less firm, Schwartz said.
What the surgery does
The surgery does cut carriers' risk of breast cancer by roughly 90%. But removing just the ovaries is effective as well – cutting a mutation carrier's breast cancer risk in half, because removing the ovaries takes away the body's main source of oestrogen.
And unlike ovarian cancer, breast cancer can often be detected early: For women with BRCA mutations who choose not to have a mastectomy, experts recommend regular screening with not only mammography, but also MRI scans, which are better at spotting breast tumours in their earliest stages.
Of the 465 women tested in the current study, 31% were found to carry BRCA mutations.
There were 100 mutation carriers who still had their ovaries, and two-thirds ultimately opted to have their ovaries and fallopian tubes removed. And of 108 mutation carriers who still had at least one breast, 37% chose to have a mastectomy.
(Most of the women in the study had already been diagnosed with breast or ovarian cancer when they decided to have BRCA testing, so some had previously had one breast or their ovaries removed.)
The US Preventive Services Task Force, an expert panel supported by the federal government, recommends that women with certain family-history patterns of breast or ovarian cancers consider BRCA testing.
That includes women who've had: two first-degree relatives (mother, sister or daughter) diagnosed with breast cancer, one of whom developed the disease by age 50; three or more first- or second-degree relatives diagnosed with breast cancer at any age; two or more first- or second-degree relatives with ovarian cancer.
Figures of women who can meet the criteria of BRCA
About 2% of US women would meet the criteria for considering BRCA testing, according to the USPSTF.
According to Schwartz, the current findings "lend credence" to the belief that BRCA testing will ultimately make a difference in carriers' risk of developing breast and ovarian cancers, and possibly extend their lives.
The primary limitation of the study, he said, is that all of the women were tested and received genetic counselling at a single medical centre. "Out in the world, the results may be different," Schwartz said.
Individual doctors can, and increasingly are, ordering BRCA testing. And women may or may not get the genetic counselling that's recommended for helping them decide what to do with the test result.
And that result is often not straightforward. Many women get what's called an "inconclusive" or "uninformative" result: They do not have a known BRCA mutation, but the possibility that they have some genetic abnormality cannot be ruled out.
That's in contrast to a "true negative" BRCA result – where a woman tests negative for mutations that had previously been found in a family member.
For women with an inconclusive result, Schwartz said, genetic counselling can help them decide what to do.
If their family history of breast or ovarian cancers is very strong, it might be assumed that there is some sort of genetic risk. So they might still consider preventive surgery or possibly regular MRI screening for breast cancer.
(Reuters Health, Amy Norton, August 2011)