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International report underscores mammography's benefits — for women over age 50

mammogram
REUTERS/Enrique Castro-Mendivil
Mammography screening among women aged 50 to 69 was associated with a 40 percent reduction in the relative risk of death from breast cancer.

An international group of cancer experts issued a major report this week in which it said that there’s good scientific evidence that mammography screening for breast cancer benefits women aged 50 to 74, but that such evidence is “limited” for women in their 40s.

If that finding sounds familiar, it’s because it’s pretty much what the U.S. Preventive Services Task Force (USPSTF) said in 2009 about mammography screening.

Back then the USPSTF’s panel of experts were widely vilified, with politicians, pundits and others declaring outrage at the suggestion that research did not support routine mammograms for women in their 40s. The fear-mongering included charges of “gender genocide” and “healthcare rationing.”

We appear to have come a long way since then. The new report, which was compiled by the International Agency for Research on Cancer (IARC) and published in the New England Journal of Medicine (NEJM) on Wednesday, garnered a lot of headlines, but only scattered moments of fear-mongering.

Updating the evidence

The 29 cancer experts from 16 countries who put together the NEJM report wanted to update their last review of the evidence on breast-cancer screening, which was done in 2002. They noted that there have been improvements in screening technology since then, as well as additional studies.

For their current review, the experts relied on randomized control trials (the “gold standard” of research) and recent, high-quality observational studies.

Here are their key findings: 

  • Mammography screening among women aged 50 to 69 was associated with a 40 percent reduction in the relative risk of death from breast cancer. The evidence does not provide a clear answer, however, on how often the women need to be screened to receive the maximum benefit. (The USPSTF experts recommend that women in this age group undergo screening every other year.)
  • The evidence was also “sufficient” that screening reduces the risk of dying from breast cancer for women aged 70 to 74. The report does not quantify that risk reduction, however.
  • Among women aged 40 to 49, the evidence that screening saves lives is “limited.” In other words, no conclusions can be drawn about whether the benefits outweigh the harms in screening women in this age group.
  • For women under the age of 40 or older than 69, the evidence that mammography screening is effective at saving lives is “inadequate.”
  • The risk of “false positives” — a screening result that comes up positive for breast cancer but that turns out to be in error on further investigation — occurs in about 20 percent of women who are screened 10 times between the ages of 50 and 69. Less than 5 percent of these false positives lead to an invasive procedure, such as a needle biopsy.
  • Up to 11 percent of women who are diagnosed with breast cancer through screening are overdiagnosed — their breast tumor is diagnosed as cancer when, in actuality, it never would have harmed them.
  • One to 10 of every 100,000 women who have a mammogram will develop breast cancer from the radiation received during the screening. For women aged 50 to 69, this risk is 100 times smaller than the risk of dying from breast cancer if they do not receive screening.

Other findings

The experts also concluded that the evidence is inadequate regarding whether ultrasound technology increases the early detection of breast cancer. Nor did the evidence show that adding magnetic resonance imaging (MRI) to the screening process for women at high-risk for breast cancer saved lives. Both these technologies were found to increase the risk of false positives, however.

In addition, the experts reported a lack of good evidence that either breast self-exams or routine breast exams by physicians reduces the risk of dying from breast cancer.  

It’s important that women have full and unbiased information about the risks and benefits of mammography screening so that they can make an informed choice. We need facts, not fear-mongering.

You can read the IARC’s report in full on the NEJM website.

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