Women with certain genetic mutations that greatly raise their risk of breast and ovarian cancer can cut the risk by as much as 80 percent if they get their ovaries removed by age 35, a new study suggests.

It’s the first study to show just how much the operation can do to lower the risk of cancer, and it’s the first to put such a clear age on the benefits.

It's a finding so striking that the researchers think ovary removal should become standard for anyone with so-called BRCA1 mutations.

“This really validates for those of us who take care of women who have a high-risk BRCA1 … gene, that removing the ovaries and fallopian tubes really does have a positive impact on that woman, reduces her risk of ovarian cancer tremendously and also improves her survival,” said Dr. Ursula Matulonis of the Dana Farber Cancer Institute in Boston, who was not involved in the study.

It’s not an easy decision. Having the ovaries out, an operation called an oophorectomy, throws a young woman into instant and permanent menopause. But the study, published in the journal of Clinical Oncology, suggests it is worth all the awful side-effects, which include a likely end to a woman’s childbearing years.

Many women with BRCA mutations already get their breasts removed long before any sign of cancer — actress Angelina Jolie was one of them, having her breasts removed at age 37.

Nicole Armstrong knew she was at risk because her grandmother died so young. “So I always thought, ‘OK, I have an increased risk. Instead of going for mammograms at 50, I have to go around 40,” the 28-year-old, who lives in Easton, Pa., told NBC News.

Then her 30-year-old sister Catrina walked into the kitchen in 2009 saying she had a painful lump under her arm.

Catrina was developmentally disabled and couldn’t explain clearly. “So my dad felt under her arm and he looks at me and doesn't say anything just mouths to me, ‘There's a lump,’” Nicole said.

It was Stage 4 breast cancer. Catrina died two years later. Testing showed she had a BRCA mutation. It turns out Catrina and Nicole’s father, Douglas Armstrong, inherited the mutation from his mother and passed it to his daughters.

Cancer experts have been debating whether to screen for many cancers, but in the case of people with a strong family history and known mutations, it’s becoming clear that preventive surgery is a good option.

“To me, waiting to have an oophorectomy until after 35 is too much of a chance to take,” said Dr. Steven Narod of the University of Toronto in Canada, who led the study. “These data are so striking that we believe prophylactic oophorectomy by age 35 should become a universal standard for women with BRCA1 mutations.”

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Narod and colleagues studied nearly 5,800 women from seven countries, including Canada and the United States, starting in 1995 and lasting until 2011. They all had mutations to the BRCA1 and BRCA2 genes, which are well known to raise the risk of breast, ovarian and other cancers.

Nicole Armstrong, 28, and her father both have the BRCA1 gene.

Just over 2,000 of the women had already had their ovaries removed and another 1,390 had them taken out during the study time. More than 2,270 chose not to have their ovaries taken out.

The women who had their ovaries taken out lowered their risk of ovarian cancer by 80 percent, the researchers found. But just for women with certain BRCA1 mutations.

Women with BRCA2 mutations didn’t benefit as much. BRCA1 and BRCA2 mutations are most common among Jews of Ashkenazi decent — at least 2 percent of these descendants of Eastern European Jews have the mutations. They are less common in the general U.S. population, but not enough testing has been done to put a firm estimate on it.

BRCA mutations are among dozens of other genetic mutations that raise the risk of breast or ovarian cancer. About 12 percent of all women will develop breast cancer during their lives, but 55 to 65 percent of women with a BRCA1 mutation will, according to the National Cancer Institute.

And while just 1.4 percent of all women will get ovarian cancer, 39 percent of those with a harmful BRCA1 mutation will.

"These results could make a real difference for women with BRCA mutations, who face tough decisions about whether and when to undergo a prophylactic oophorectomy,” said Dr. Don Dizon of Harvard Medical School and a member of the American Society for Clinical Oncology. “For women with BRCA1 mutations, these results suggest that surgery should be performed as soon as it is practical."

Women with BRCA mutations have already been thinking about surgery. Rates of women who are opting for preventive mastectomies have increased by an estimated 50 percent in recent years, experts say. And surveys show they are happy with the decision.

But first, women need to know they are at risk, and that’s usually by knowing family history.

Catrina Armstrong died of breast cancer found at age 30. Her sister will now have surgery to protect herself. Armstrong family

Nicole Armstrong knew she should get tested, but she was just 24 and was afraid to learn the bad news. “I refused, refused, refused to get the testing done. I didn't want to know what was going to happen to me,” she said.

She waited nine months before getting tested, then had both breasts removed, although she had no sign of cancer. Now Nicole must make a decision about her ovaries.

“I don't have any children so, the thought of me, you know, being 28 now and I have six years to have my ovaries removed and have a child somehow in the middle of all of that,” she said. “I think about what if I have fertility issues?”

But she’ll do it, in part to remember her sister Catrina. “Not only am I doing this for myself, to keep myself healthy and try to live a full life, and you know, it's for her,” said Armstrong, who gets support from a non-profit called Facing Our Risk of Cancer Empowered.

“She went through so much, and had she not, it could be me who at 30, you know, got the news that I had breast cancer.”

“I try not to think about it too much because it is, it's overwhelming.”

Narod’s group had previously shown that having the ovaries removed lowered the risk of breast cancer by 48 percent in women with BRCA mutations, probably because it stops the production of the hormone estrogen, which often fuels breast cancer.

But the idea remained somewhat controversial, in part because treatments are so good. Survival rates for breast cancer are 93 percent if it’s caught at the earliest stages.

However, it’s a different picture for ovarian cancer, which is usually not detected until it has spread because the symptoms it causes are so vague — bloating and discomfort, mostly. There is no good screening test yet for ovarian cancer, which is the deadliest women’s cancer, killing 15,000 women a year in the United States. Only 46 percent of women diagnosed with ovarian cancer survive for five years or longer.

BRCA mutations also raise the risk of cancer for men, and Douglas Armstrong is watching out for his own health. But mostly, he says, he’s worried about Nicole. “Yeah, I have an increased chance of getting cancer, of breast cancer, of prostate cancer, but not as much as my daughter,” he said.

He’s encouraging Nicole to have her ovaries removed. “I definitely want her to get it done … but my Mom and I would like a grandchild before she does it,” he said.

Nicole Armstrong, who has no sign of cancer and who has a boyfriend but isn’t married, says she wants children. “I try not to think about it too much because it is, it's overwhelming,” she says.

NBC News Producer Jane Derenowski, Researcher Judy Silverman and NBC News Channel Producer Erin Sykes contributed to this report.