Canadian Study Questions Value of Mammograms for Women Aged 40 to 59; Experts Say Research Is Flawed

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Several large studies, including a review by the U.S. Preventive Services Task Force in 2009 and a study on the causes of death in the United Kingdom in 2013, have questioned the value of screening mammograms.

On the other hand, a group of researchers from around the world reexamined the data from four large studies on the risks and benefits of breast cancer screening and presented their results at the 2013 San Antonio Breast Cancer Symposium. They found that the benefits of screening mammograms are more consistent across these studies than has been previously reported. They also found that all the studies showed a sizable reduction in deaths from breast cancer because of screening mammograms.

Doctors who question the value of mammograms say that while mammograms do save lives, for each breast cancer death prevented, three to four women are overdiagnosed. Overdiagnosis means either:

  • a screening mammogram finds a suspicious area that would have been eventually diagnosed as cancer by other means, without any effect on prognosis
  • a screening mammogram finds a suspicious area that never would have affected a woman’s health if it hadn’t been found or treated

False positive results from screening mammograms also have helped fuel the debate about the value of breast cancer screening. When a mammogram shows an abnormal area that looks like a cancer but turns out to be normal, it’s called a false positive. Ultimately the news is good: no breast cancer. But the suspicious area usually requires follow-up with more than one doctor, extra tests, and extra procedures, including a possible biopsy. There are psychological, physical, and economic costs that come with a false positive.

These studies and the resulting stories in the media have fueled an ongoing debate about the value of screening mammograms.

Now a new Canadian study has found that after 25 years of follow-up, annual mammograms didn’t reduce the number of women aged 40 to 59 who died from breast cancer, compared to women who didn’t get mammograms and got only a physical exam. Still, many experts were quick to criticize the study as flawed and misleading.

The research was published in the Feb. 11, 2014 issue of BMJ. Read the abstract of “Twenty five year follow-up for breast cancer incidence and mortality of the Canadian national Breast Screening Study: randomized screening trial.”

In the study, researchers randomly assigned 89,835 Canadian women aged 40 to 59 to have an annual mammogram or not for a period of 5 years. All the women aged 50 to 59 had a physical breast exam each year, no matter whether they were in the mammogram group or not. Women aged 40 to 49 who were in the mammogram group also had a physical breast exam each year. Women aged 40 to 49 who weren’t getting mammograms had a physical breast exam when the study started and then received standard care. Standard care means they went on to have mammograms and any needed follow-up procedures after the 5-year study period was over.

During the 5-year period when the women in the mammogram group were being screened:

  • 666 breast cancers were diagnosed in women in the mammogram group
  • 524 breast cancer were diagnosed in women in the no mammogram group
  • 180 women in the mammogram group died of breast cancer
  • 171 women in the no mammogram group died of breast cancer

During the entire 25 years of the study:

  • 3,250 women in the mammogram group were diagnosed with breast cancer
  • 3,133 women in the no mammogram group were diagnosed with breast cancer
  • 500 women in the mammogram group died of breast cancer
  • 505 women in the no mammogram group died of breast cancer

The researchers concluded that annual mammograms don’t reduce the number of women aged 40 to 59 who die from breast cancer any more than an annual physical exam.

Still, there are some questions about this study. As soon as it was published, the American College of Radiology and the Society of Breast Imaging released a joint statement saying the study was “an incredibly misleading analysis based on the deeply flawed and widely discredited Canadian National Breast Screening Study.” The joint statement went on to say that the quality of the mammography used in the Canadian study was poor and that the study used second-hand mammography machines. The organizations also said, “In this latest BMJ paper, only 32% of cancers were detected by mammography alone. This extremely low number is consistent with poor quality mammography. At least two-thirds of the cancers should be detected by mammography alone.”

Dr. Larry Norton, Memorial Sloan Kettering’s deputy physician-in-chief for Breast Cancer Programs and a member of the Breastcancer.org Professional Advisory Board, cautioned women not to be influenced by headlines.

“This is further follow-up of a flawed study,” Norton said. “There are no new data here, so it should not influence any changes in screening recommendations.”

If you're 40 or older and have an average risk of breast cancer, yearly screening mammograms should be part of your healthcare. If your breast cancer risk is higher than average, you should talk to your doctor about a more aggressive breast cancer screening plan that makes the most sense for your particular situation.

There's only one of you and you deserve the best care possible. Don't let any obstacles get in the way of your regular screening mammograms:

  • If you're worried about cost, talk to your doctor, a local hospital social worker, or staff members at a mammogram center. Ask about free programs in your area.
  • If you're having problems scheduling a mammogram, call the National Cancer Institute (800-4-CANCER) or the American College of Radiology (800-227-5463) to find certified mammogram providers near you.
  • If you find mammograms painful, ask the mammography center staff members how the experience can be as easy and as comfortable as possible for you.

For more information, visit the Breastcancer.org Mammograms pages.


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