By Amy Norton
WEDNESDAY, June 3, 2015 (HealthDay News) -- Adding to the debate about the benefits of mammography screening before age 50, a new research review finds "limited" evidence that screening prevents breast cancer deaths among women in their 40s.
The results come from the International Agency for Research on Cancer, which asked experts from 16 countries to look at the latest evidence on breast cancer screening.
What they found largely confirmed what experts have long said: For women ages 50 to 75, routine mammograms reduce the risk of dying from breast cancer.
For women in their 40s, however, the agency found only limited evidence of such a benefit.
Still, one panel member said that conclusion was far from unanimous.
"The group was split down the middle, at least when it came to women ages 45 to 49," said Robert Smith, vice president of the American Cancer Society. "Half of us thought the data were sufficient to say [screening mammography] reduces breast cancer mortality. Others were not persuaded."
The report, published in the June 4 issue of the New England Journal of Medicine, reflects a longstanding debate.
In 2009, the U.S. Preventive Services Task Force ignited a controversy when it changed its recommendations on mammograms -- which had long advised women to have screening every one to two years, starting at age 40.
The revised guidelines now say routine screening should begin at age 50 and be done every two years. The panel said women in their 40s should discuss the pros and cons of mammography screening with their doctors, then make an informed decision.
However, the cancer society and the American College of Obstetricians and Gynecologists still urge women to get yearly mammograms, starting at age 40.
The problem, the task force said, is that breast cancer screening can cause harm, so there should be strong evidence that the benefits outweigh those risks.
The risks include false-positive results that trigger further, sometimes invasive tests, and needless anxiety. But the bigger concern, experts say, is over-diagnosis and overtreatment.
Mammography catches tiny tumors, some of which may never progress to the point of threatening a woman's life. But because there is no way to predict which tumors are dangerous, women almost always go through treatment.
Smith stressed all women should be fully informed of the downsides going into screening. But as far as the cancer society is concerned, he said, the evidence of benefit to women in their 40s is sufficient.
"Across the world, people interpret the data differently," Smith noted. "And that's partly based on the resources available for mammography screening [in a given country]."
It is true that screening carries less benefit for women in their 40s versus older women, Smith said.
That's largely because their risk of breast cancer is lower. The average 40-year-old has a 1.5 percent chance of developing the disease in the next 10 years, while a 60-year-old has a 3.5 percent chance, according to the U.S. Centers for Disease Control and Prevention.
Age alone should not determine whether a woman undergoes mammography screening, said Joni Avery, a spokesperson for Susan G. Komen, the Dallas-based nonprofit organization that funds breast cancer education and research.
"Any screening recommendations must account for an assessment of an individual's risk," said Avery.
"In our opinion," she said, "women should be talking to their doctors about screening well before their 40s, to find out if they have a high risk of developing breast cancer, or have other personal health issues that may require a specialized screening program."
That specialized screening may include yearly MRI scans in addition to mammograms. The cancer society recommends that approach for women at high risk of breast cancer because of mutations in the BRCA1 or 2 genes, or a very strong family history of breast cancer.
In its current review, the agency for research on cancer said there is "inadequate" evidence that enhanced screening benefits high-risk women.
But that, Smith stressed, was based on a lack of randomized clinical trials. Such studies would require researchers to randomly assign high-risk women to undergo the screening regimen or not -- which would be ethically impossible.
"A trial like that is never going to happen," Smith said.