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Weighing the Risks and Benefits of Screening Mammography

December 03, 2012

Weighing the Risks and Benefits of Screening Mammography

Two recent research articles have questioned the value of mammograms and opened up a dialogue about possible benefits and harms of screening for breast cancer. One study looked at mammography in the general population and the other in high-risk young women. Both studies raise interesting concerns, but neither provides the definitive answers needed to dismiss mammography as a screening tool.

The first article looked at large population-based statistics over three decades and concluded that although mammograms found more early cancers, they did not lead to a similar reduction in cancers diagnosed at a late stage. The authors conclude that screening mammograms are leading to the overdiagnosis and treatment of a substantial number of women. Based on these conclusions, the authors question the benefit of screening mammograms for the general population.

In reviewing the research and conclusions of this article, we had several concerns:

  • The study combines DCIS (a type of non-invasive cancer) and stage I breast cancer in the same category as “early-stage” breast cancer even though stage I breast cancer behaves differently than DCIS.
  • The study was not designed to distinguish women by age or outcome.
  • The authors imply that earlier diagnosis equals overtreatment. However, there are tests available that look at tumor samples to better determine which early-stage cancers are more likely to behave aggressively and which women would benefit from further treatment. If we don’t find these early cancers through screening then we lose an opportunity to tell which ones are more likely to become advanced.
  • Changing screening practices to lower the number of women that are overdiagnosed could lead to an increase in women being diagnosed at a stage requiring more extensive treatment.

In an emotionally-charged opinion piece in the New York Times entitled “Cancer Survivor or Victim of Overdiagnosis?” one of the study authors made these recommendations:

“We must redesign screening protocols to reduce overdiagnosis or stop population-wide screening completely. Screening could be targeted instead to those at the highest risk of dying from breast cancer—women with strong family histories or genetic predispositions to the disease. These are the women who are most likely to benefit and least likely to be overdiagnosed.”

Personalizing screening recommendations based on risk makes sense. Unfortunately, the health care community doesn’t always use the risk-assessment tools available to help identify women in the highest risk category. Many women with BRCA mutations do not learn that they are high risk until they are diagnosed with breast cancer, often based on a screening mammogram. Changing screening guidelines will disproportionately hurt these women in our community.

The author also suggests:

“What should be done? First and foremost, tell the truth: women really do have a choice. While no one can dismiss the possibility that screening may help a tiny number of women, there’s no doubt that it leads many, many more to be treated for breast cancer unnecessarily. Women have to decide for themselves about the benefit and harms.” 

As someone on the receiving end of a mammogram call-back, and ultimately, a breast cancer diagnosis, I understand how anxiety-provoking screening and biopsies can be. Relaying to women the possible consequences if their screening finds an abnormality is critical. A balanced discussion should also include information about the possible consequences of a delayed diagnosis, the additional treatment that might be required for later-stage diagnosis, and the existence of decision-support tools such as Oncotype DX and Mammaprint and other technologies that can help determine which early stage cancers, once found, are more likely to behave aggressively.

The author goes on to state the following:

“But health care providers can also do better. They can look less hard for tiny cancers and precancers and put more effort into differentiating between consequential and inconsequential cancers.”

Research is ongoing to determine which cancers are more or less likely to behave aggressively. Currently we do have the technology to test breast tumors for markers of aggressive behavior. But these tests require detecting the tumors and sampling them through biopsy. I strenuously disagree with his suggestion that doctors “…look less hard for tiny cancers and precancers...”  and the assertion that diagnosing breast cancer at early stages equates to overdiagnosis and treatment. If we pass up the opportunity to find these abnormalities with mammograms and biopsy, we deprive women of critical information on which to base their health care decisions.

A second study raised interest and alarm about mammograms in high-risk women younger than age 30.  In this study researchers concluded that exposure to ionizing radiation before the age of 30 is associated with an increased risk of breast cancer. Closer review of this second article, however, highlights areas that warrant more examination before we eliminate mammograms as screening tools for young previvors. Questons have also been raised about this study’s design and conclusions. Some of the concerns include:

  • The increased breast cancer incidence when comparing those with no radiation exposure to those with any exposure between ages 20-39 was not statistically significant.
  • The estimated radiation doses used in this paper were self-reported and therefore subject to "recall bias.”
  • Although MRIs are very sensitive for finding abnormalities in the breast, mammograms find microcalcifications, small changes that can indicate an early cancer which are sometimes missed by MRIs. There is concern that in eliminating mammograms, some of early cancers might be missed until they are more advanced.

Members of the FORCE Scientific Advisory Board agree that the current study addresses a critical question that must be answered, but generally feel that the results of the current study are not conclusive. More research is needed to clarify the possible link between radiation exposure and increased cancer risk in BRCA1/2 carriers; expert panels will continue to update screening guidelines based on those future results.

Although imperfect, mammography does save lives, and we must apply all the means we have to save as many lives as we can.  More research is needed to determine if the harms of diagnosis and treatment outweigh the consequences of missing cancers, and to provide a clearer understanding of how many more lives will be lost if guidelines are changed to remove the recommendation of screening mammography. If policy-makers choose a shared decision-making strategy for breast screening, all factors must be shared with each woman to help her make her own informed decision. In order to maximize breast cancer outcomes, the health care community needs to assure that women have access to qualified experts who can help assess their risk for breast cancer. For high-risk women, experts concur that the benefits of screening with mammograms and MRI outweigh the risks.

Posted in: Research , Risk Management
Tags: BRCA , Breast Cancer , Hereditary Cancer Research , BRCA1 , BRCA2 , Previvor , Young Survivor , HBOC , USPSTF , Screening And Prevention

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