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A sweeping U.S. study published on Nov. 22, 2012 in the New England Journal of Medicine shows that mammograms have done surprisingly little to catch deadly cancers before they spread. At the same time, they have led more than a million women to be treated for growths that never would have threatened their lives. In this 2010 file photo, a radiologist uses a magnifying glass to check mammograms for breast cancer in Los Angeles. (Damian Dovarganes/AP, File)

Women over 40 are routinely advised to have yearly mammograms, and it’s widely believed that having one is key to protecting a woman’s health.

Although experts agree that diagnostic mammograms are beneficial (cases where there is a breast lump or other symptoms), there is much controversy about screening mammograms, which are performed on women with no signs of cancer. Mammograms detect breast cancer, although many people believe mistakenly that they prevent breast cancer.
We now know that the mortality benefits remain quite small.

Eight trials performed in the United States, Canada and Europe have evaluated the ability of screening mammograms to decrease the death rate from breast cancer, as well as overall mortality. Looking at the overall death rate, not just death from breast cancer, is essential, because this approach also evaluates whether the screening test and any subsequent treatment may be causing other harms.

Although experts agree that diagnostic mammograms are beneficial, there is much controversy about screening mammograms, which are performed on women with no signs of cancer.

Overall, the early studies showed a 30 percent reduction in the risk of dying from breast cancer in women who were screened by mammography. In 2001, a critical review of all eight trials by the Cochrane Collaboration found that six of them were sufficiently flawed to invalidate their results. The Cochrane Collaboration then pooled the results of the two remaining studies and found no evidence to support the use of screening mammography. The U.S. Preventive Services Task Force (USPSTF) evaluated the trials also. Although recognizing many of the same flaws, the USPSTF felt only one trial was sufficiently flawed to be invalidated. They pooled the results of the remaining trials and found a 16 percent reduction in the risk of dying of breast cancer in the women in the screened group.

The meta-analysis published in 2006 by the Cochrane Collaboration confirmed that screening does slightly reduce breast cancer mortality, but that it also leads to over-diagnosis and overtreatment of breast cancer. They concluded:

“(F)or every 2000 women invited for screening throughout 10 years, one will have her life prolonged. In addition, 10 healthy women, who would not have been diagnosed if there had not been screening, will be diagnosed as breast cancer patients and will be treated unnecessarily. It is thus not clear whether screening does more good than harm.”

In a recent issue of the New England Journal of Medicine, Dr. Archie Bleyer and Dr. Gilbert Welch summarized the latest analyses as follows:

“Despite substantial increases in the number of cases of early-stage breast cancer detected, screening mammography has only marginally reduced the rate at which women present with advanced cancer.”

And this is the key to meaningful breast cancer screening — that we reduce the rate at which women have to be treated for late stage cancer.

When the data for women under 40 were studied (these are women who generally don’t get regular mammograms), Dr. Welch and Bleyer wrote:

“There was a larger relative reduction in mortality among women who were not exposed to screening mammography than among those who were exposed. We are left to conclude, as others have, that the good news in breast cancer — decreasing mortality — must largely be the result of improved treatment, not screening.”

Dr. Susan Love, a long time clinician and researcher, would like to see less emphasis on screening and more focus on cancer prevention and treatment for the most aggressive cancers. (Roughly 15 percent to 20 percent of breast cancers are deadly.) “There are still 40,000 women dying every year,” Dr. Love notes. “Even with screening, the bad cancers are still bad.”

Mammography, like other detection tools, is imperfect (it misses about 20 percent of lumps due to dense breasts and other factors).

As Donald Berry, a biostatistician at M.D. Anderson Cancer Center in Houston, has pointed out: “Most breast cancers are not lethal, however found,” Dr. Berry said. “Screening mammograms preferentially find cancers that are slowly growing, and those are the ones that are seldom deadly. Getting something noxious out of the body as soon as possible leads women to think screening saved their lives. That is most unlikely.”

The challenge now is to make more widespread the use of techniques that help clinicians identify biological markers that will distinguish between the lethal and benign types of tumors. This appears to be the next big advance in reducing mortality from breast cancer.

Mammography, like other detection tools, is imperfect (it misses about 20 percent of lumps due to dense breasts and other factors). Some would consider it a very weak detection tool, and given the harms of overtreatment (for example, unnecessary chemotherapy and radiation treatments), it is not surprising that some women will want to forego screening mammography.

Women need to carefully consider these factors and decide for themselves what would be best, although friends, caregivers, and even commercial interests may tell them that having routine mammograms is the only rational choice. What really helps is knowledgeable and supportive counseling.

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Tags: Women's Health

The views and opinions expressed in this piece are solely those of the writer and do not in any way reflect the views of WBUR management or its employees.

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  • X-Ray

    As one who has taken many Health Physics courses (dealing with radiation), I
    wonder how may cancers are induced by the radiation absorbed from the cancer
    screening test itself.

    • Ismur

      Robust evidence showed that any dose of ionizing radiation increases the risk of cancer, particularly breast cancer (read Rolf Hefti’s e-book “The Mammogram Myth: The Independent Investigation Of Mammography The Medical Profession Doesn’t Want You To Know About”). Therefore, mammography has caused cancer in many women because the test is performed widely.

  • Kate

    I can only say that my breast cancer experience completely negates this study. At intervals, I had stage 4 in one breast, and stage 3 in the other, both discovered after routine mammography. I had no symptoms that would indicate my condition prior to the mammograms. I have received appropriate, consistent treatment for 11 years since diagnosis.

    • Jenna Smith

      If you underwent routine mammograms, ow did those tumors get to stage 3 and stage 4? You also don’t know if those tumors ever would have caused you any problem at all, and you don’t know if treating them at the stages they were found vs. when the tumors would have been palpated made any difference at all. It’s a poor test, but people such as yourself who don’t understand that one anecdote does not negate valid analysis of disease outcome in a population will continue to push for more screening. Screening is most useful for lining the pockets of radiologists and oncologists, not for saving lives.

  • Pam

    The over-reliance on such things as Mammographies may distract from crucial measures such as diet and exercise,both very powerful health measures.
    The food available(and eaten by) health professionals in medical centers and clinics and the frantic,treadmill atmosphere does not bode well for their health or ours.

  • Leslie

    I read a great blog on this by a gynecologist at http://www.mcwhertermd.com

  • Mary Saltz, MD

    If you are interested in what a seasoned female radiologist who has read 1000s of mammograms thinks take a peek at my blog

    http://hospitalradiologypartnersblog.com/author/hospitalradiologypartners/

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