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 program between women eligible for mammography screening and women outside the screening age (younger and older).

The team analyzed the data of women aged 30-89 using the Cancer Registry of Norway and divided them in three age groups within the pre- and post-screening implementation periods: women eligible for screening, younger ineligible women, and older ineligible women.

They identified 4,903 women who were diagnosed and died of breast cancer within the same age-period group from 1987-2010.

All three age groups showed a significant decrease in breast cancer mortality after implementation of screening compared to the pre-screening period. However, this decrease was comparable between women eligible for screening and ineligible women.

The team noted that the application of different methods of analysis did not affect the results.

“The important result is that we do not find a beneficial effect of breast cancer screening any longer,” and “the better the treatment methods become, the less benefit screening has,” Henrik Støvring, the study’s senior author, said in a press release.

These findings suggest that screening does not prolong the overall life of women with breast cancer.

Støvring explained that women who undergo screening live longer because all breast cancer patients live longer nowadays, because “we now have better drugs and more effective chemotherapy, and … the healthcare system reacts faster than it did a decade ago,” but it does not seem that “fewer women die of breast cancer as a result of mammography screening.”

The team noted that additional and similar studies are necessary to confirm these results and to confirm that improved treatment and other changes are plausible explanations.

Støvring also pointed out that the implementation of mammography screening programs has contributed to the increased number of overdiagnoses of breast cancer in developed countries, meaning that patients with tumors that are benign or so slow-growing that they would not have become life-threatening still undergo surgery and chemotherapy.

He suggested that the regular breast examination by a doctor through palpation, instead of mammography screening, could prevent this overdiagnosis.

One comment

  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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