Mammography Screening Does Not Reduce Breast Cancer Mortality, Study Suggests

Mammography Screening Does Not Reduce Breast Cancer Mortality, Study Suggests
While fewer women die from breast cancer now compared to a decade ago, the decline is no longer associated with mammography screening, but with improved treatment and healthcare, a Norwegian study suggests. The study, “Effect of organized mammography screening on breast cancer mortality: A population‐based cohort study in Norway,” was published in the International Journal of Cancer. Before the implementation of mammography screening programs, randomized clinical studies highlighted the importance of this type of screening, as it was shown to decrease breast cancer mortality by 19-20%. Currently, the value of mammography screening may not be the same, considering that substantial improvements have been made in terms of treatment and that people are now more aware of breast cancer and the importance of breast self-examination. However, different observational studies have reached inconsistent results in terms of the current benefit of breast cancer screening, with benefits ranging from zero to 43%. This discrepancy may be due to difficulties in separating the benefit associated with the introduction of mammography screening programs from that of these simultaneous changes that may influence breast cancer mortality. Researchers at Oslo University now have assessed the benefits of the mammography screening program in breast cancer mortality in Norway through a method that allows the differentiation of these two effects. They compared breast cancer mortality before and after the implementation of the screening progr
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  1. Paula B Gordon, OBC, MD, FRCPC, FSBI says:

    This study cannot come to any conclusions about the value of mammography because of how they obtained the data. They looked at the Cancer Registry of Norway, and the deaths from breast cancer during 3 periods of time, but they do not know which women received a mammogram.
    They made several assumptions:
    1. that no women had mammograms prior to the implementation of their screening program,
    2. that all eligible women had mammograms after implementation, and
    3. that none of the ineligible women had mammograms after implementation.
    But mammography was available in Norway prior to the screening program opening, and it’s very likely that some women had mammograms prior to implementation. It’s also highly likely that may “ineligible” women outside the screening program. And most importantly, it’s highly probable that not all “eligible” did attend. In that scenario, an “eligible” woman who does not attend, who does get breast cancer, may have it diagnosed at a more advanced stage, and therefore her death is not postponed. That is, she dies during the study period. But the researchers don’t know that she did not attend; indeed they assume that she did, so her death is included in the “mammogram group,” and the researchers mistakenly conclude that mammography doesn’t reduce mortality.
    In randomized trials, the investigators knew who did and did not attend. And the RCT proved mortality reduction in spite of contamination and noncompliance. The magnitude of mortality reduction is even better shown in observational studies, although selection bias does occur. Readers should know that observational trials show 40-50% mortality reduction among screened women, and should decide whether to participate in screening based on these statistics.

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