Even people who carry genetic changes that put them at higher-than-average risk of breast cancer can lower that risk — sometimes by a lot, researchers said Thursday.
They predict that close to 30 percent of breast cancer cases among white women could be prevented if all the women did just four things: avoided smoking, drank very little alcohol, kept a healthy body weight and skipped hormone replacement therapy.
"Overall, we estimated that up to 28.9 percent of all breast cancers could be prevented if all white women in the U.S. population were at the lowest risk from these four modifiable risk factors," Nilanjan Chatterjee of the Johns Hopkins Bloomberg School of Public Health and colleagues wrote in their report, published in the Journal of the American Medical Association's JAMA Oncology.
Chatterjee is quick to say the calculation is not ready for the average person to use yet. But he says the findings offer hope to people who may find out they have a "cancer gene" and feel they are doomed. "Lifestyle plays such an important role even in the context of genetic risk," he told NBC News.
With DNA tests becoming more common, easy to get done and coming down in price, more and more people will find out they have a rare mutation that raises their cancer risk, Chatterjee said. "There is so much in the news that everything is determined by genetic risk," he said.
His finding shows there is something people can do. And there's no risk to not smoking, keeping at a healthy weight, limiting drinking or avoiding HRT.
"It doesn't hurt anybody but what happens sometimes is that people lack motivation," Chatterjee said.
The team studied the cases of more than 40,000 women taking part in breast cancer and other health studies. They looked at 92 common mutations known to raise breast cancer risk. They left out the two best-known breast cancer risk genes — BRCA1 and BRCA2 — because they're so clearly defined and studied.
Chatterjee said his team wanted to address the thousands of women who don't have BRCA1 and BRCA2 mutations who find out they have other mutations that may raise their breast cancer risk. And he said these 92 common mutations, which women usually don't know about, account for more cases of breast cancer than the BRCA genes do.
Future studies should add those in, he said, as well as other known breast cancer genes.
Eventually, the model might be used to help women know if they need to start getting mammograms early if they're at especially high risk, or if they can spread out their mammograms later in life because they're at lower risk.
"Our analysis shows that use of a model based on most known risk factors can change the recommendation for screening for a substantial fraction of the population, compared with using only age-based criteria," the team wrote.
They calculated that 16 percent of 40-year-old women have the breast cancer risk of someone 10 years older and might want to get mammograms earlier than recommended. And they said 32 percent of 50-year-old women have a lower-than-average risk for their age. "These women benefit least from screening and may benefit from additional counseling about risk of false-positive results," the team wrote.
The American Cancer Society estimates that more than 230,000 U.S. women will be diagnosed with breast cancer this year, that 40,000 women will die from it and that one in eight women will be diagnosed at some point in their lifetimes.
The team said they calculated risks for different groups. "The absolute cumulative risk of a 30-year-old white woman in the United States developing invasive breast cancer over the next 50 years is 11.3 percent on average," they wrote.
Three outside experts agree that it's too soon to use the calculation in real life. "It remains premature— in our opinion — to use this model to support such clinical decision-making," Dr. William Dupont, Dr. Jeffrey Blume and Dr. Jeffrey Smith of Vanderbilt University wrote in an editorial.
But Chatterjee says there are ways to make the risk calculation better and more accurate. These include adding known risk factors such as education, breastfeeding, physical activity, conditions such as having dense breasts, and hormone levels. It will also be important to include non-white women in the calculation.
Currently, women are steered to the Gail Model to calculate breast cancer risk. It factors in age, family history of breast cancer, pregnancy history and race.