Breast-Cancer Screening

Posted by • June 12th, 2015

The International Agency for Research on Cancer (IARC) has updated its 2002 guidelines on screening for breast cancer, drawing on data from studies completed in the past 15 years.

In November 2014, experts from 16 countries met at the International Agency for Research on Cancer (IARC) to assess the cancer-preventive and adverse effects of different methods of screening for breast cancer. In preparation for the meeting, the IARC scientific staff performed searches of the openly available scientific literature according to topics listed in an agreed-upon table of contents. The full report is presented in volume 15 of the IARC Handbooks of Cancer Prevention.

Clinical Pearls

– What data are available to assess the effectiveness of contemporary mammographic screening?

The IARC working group recognized that the relevance of randomized, controlled trials conducted more than 20 years ago should be questioned, given the large-scale improvements since then in both mammographic equipment and treatments for breast cancer. More recent, high-quality observational studies were considered to provide the most robust data with which to evaluate the effectiveness of mammographic screening. The working group gave the greatest weight to cohort studies with long follow-up periods and the most robust designs, which included those that accounted for lead time, minimized temporal and geographic differences between screened and unscreened participants, and controlled for individual differences that may have been related to the primary outcome. Analyses of invitations to screenings (rather than actual attendance) were considered to provide the strongest evidence of screening effectiveness, since they approximate the circumstances of an intention-to-treat analysis in a trial.

Is there evidence of a reduction in breast cancer mortality with mammographic screening?

Some 20 cohort and 20 case-control studies, all conducted in the developed world (Australia, Canada, Europe, or the United States) were considered by the IARC working group to be informative for evaluating the effectiveness of mammographic screening programs, according to invitation or actual attendance, mostly at 2-year intervals. Most incidence-based cohort mortality studies, whether conducted in women invited to attend screening or women who attended screening, reported a clear reduction in breast-cancer mortality, although some estimates pertaining to women invited to attend were not statistically significant. Women 50 to 69 years of age who were invited to attend mammographic screening had, on average, a 23% reduction in the risk of death from breast cancer; women who attended mammographic screening had a higher reduction in risk, estimated at about 40%. Case-control studies that provided analyses according to invitation to screening were largely in agreement with these results.

Morning Report Questions

Q: Is there benefit to mammographic screening of women 70 to 74 years of age, and is there a benefit for those 40 to 44 years of age?

A: In the IARC analysis, a substantial reduction in the risk of death from breast cancer was consistently observed in women 70 to 74 years of age who were invited to or who attended mammographic screening in several incidence-based cohort mortality studies. Fewer studies assessed the effectiveness of screening in women 40 to 44 or 45 to 49 years of age who were invited to attend or who attended mammographic screening, and the reduction in risk in these studies was generally less pronounced. Overall, the available data did not allow for establishment of the most appropriate screening interval.

Table 1. Evaluation of Evidence Regarding the Beneficial and Adverse Effects of Different Methods of Screening for Breast Cancer in the General Population and in High-Risk Women.

Q: What harms are associated with mammographic screening?

A: Estimates of the cumulative risk of false positive results differ between organized programs and opportunistic screening. The estimate of the cumulative risk for organized programs is about 20% for a woman who had 10 screens between the ages of 50 and 70 years. Less than 5% of all false positive screens resulted in an invasive procedure. There is an ongoing debate about the preferred method for estimating over-diagnosis. After a thorough review of the available literature, the working group concluded that the most appropriate estimation of over-diagnosis is represented by the difference in the cumulative probabilities of breast-cancer detection in screened and unscreened women, after allowing for sufficient lead time. The Euroscreen Working Group calculated a summary estimate of over-diagnosis of 6.5% (range, 1 to 10%) on the basis of data from European studies that adjusted for both lead time and contemporaneous trends in incidence. The estimated cumulative risk of death from breast cancer due to radiation from mammographic screening is 1 to 10 per 100,000 women, depending on age and the frequency and duration of screening. It is smaller by a factor of at least 100 than the estimates of death from breast cancer that are prevented by mammographic screening for a wide range of ages. After a careful evaluation of the balance between the benefits and adverse effects of mammographic screening, the working group concluded that there is a net benefit from inviting women 50 to 69 years of age to receive screening.

3 Responses to “Breast-Cancer Screening”

  1. RIchard Chessick, M.D. says:

    What studies of this sort are there on women over 75 years of age?

  2. Frank Dundee says:

    Percentages used in measuring “effectiveness” do not take several major concerns under consideration: What percentage of women who have a detectable cancer that would have been revealed under mamography, would have lived just as long or longer without any intervention? What percentage of interventions related to mamography screening did not extend the woman’s life any longer than if undetected? And what about the percentage decrease in the quality of life for the woman and her family AFTER detection? As the saying goes, “It is one thing to have cancer, quite another to KNOW you have cancer.
    Mamography, as a screening tool, is what I consider an “almost”. The idea is a good one, but it is hit or miss. And any tool that is not upwards of 95% effective, and marketed to the public as a mandatory testing device, is no more than smoke and mirrors. The only fact revealed here is that mamography benefits the medical-industrial complex at 100%

  3. William JT Wiggins says:

    What about self examinations? I read on this site that there was no real detected benefit seen in self examinations. Is there now no benefit in advising women to do this? I figure it would be very difficult convincing them of this after all the years spent drilling this into their heads.