Spanish breast imager weighs in on Kopans' critique

April 6, 2010

I read with great interest the online article by Dr. Daniel Kopans on screening mammography

I read with great interest the online article by Dr. Daniel Kopans on screening mammography (“Why the critics of screening mammography are wrong,” posted at DiagnosticImaging.com, Dec. 4, 2009), and also the related one by Dr. Berlin.

As a breast radiologist, I have great respect and admiration for Dr. Kopans. Most of us have learned-and still learn-from his writings, but I have to say that this article seemed to me distasteful, arrogant, and contentious. As a radiologist and a European citizen, I feel deeply insulted by statements such as that many European countries do not support or encourage screening because they have lied to their populations. This is a quite strong assertion.

Decreasing breast cancer mortality as a result of mammography screening and improved therapeutics is undeniable, but many shadows are still cast over breast cancer screening, despite Dr. Kopans' views. One of them is screening premenopausal women, and that deserves more research and scientific discussion.

Of course, the age-50 limit, a sort of sticking point, is arbitrary, as is 5% for statistical significance or 80% for statistical power. But we need thresholds like these to help decision-making. We know that breast cancer behaves differently before and after menopause, and the 50-year figure is a surrogate for menopause. On the other hand, there are two randomized controlled trials addressing the screening of women under 50, both with a negative result. But this point is ignored when defenders of screening scorn people who have some doubts about it.

I do believe that disagreement in science is a way of progressing and that objectivity is a myth, as Donald Berry has pointed out. I also believe that “absolute truths” do not exist because there are a lot of circumstances that can distort them. As a European physician who works for a public health system, I can't help but think that money could be one of these circumstances. I do consider screening mammography very useful. But to the best of my knowledge, it is not an absolute truth.

Dr. Manuel Vázquez Caruncho
Breast radiologist
Complexo Hospitalario Xeral-Calde
Lugo, Spain

Kopans' response

I am being limited in the number of words I can use to respond to Dr. Caruncho's detailed concerns so I will address only the most important here. His critique is thoughtful, but not scientifically accurate.

The randomized, controlled trials (RCTs) of screening, when analyzed as they were designed to be, have always shown a statistically significant benefit for screening beginning at the age of 40.1 The age of 50 was imbued with scientifically unsupportable importance when analysts broke out women ages 40 to 49 for separate analysis,2 despite the fact that the RCTs lacked the statistical power to permit using such analyses for making medical recommendations.3 Dr. Caruncho should know that if these types of analysis were legitimate for making medical recommendations, then we should be able to examine smaller and ever smaller subgroups and would, ultimately, need only two women in a trial. This is scientific nonsense, but our National Cancer Institute (in 1993) and other governments guided their populations using these fallacious analyses. Either they were lying to their populations, or they simply did not understand scientifically appropriate trial data analysis and should not have been advising anyone.

Opponents of screening for women in their 40s take data that change gradually with increasing age and group them dichotomously (40 to 49 compared with 50 and over) as if they were two uniform groups. Kerlikowske did this, adding women in their 30s to pull down the numbers for women under age 50.4 This makes gradual changes, falsely, appear to change abruptly at the age of 50. Data grouping can be used to make any age appear to be a jumping point. What would Dr. Caruncho call this: legitimate scientific analysis or manipulation of data? There are no ungrouped data showing that any of the parameters of screening change abruptly at the age of 505 or at menopause.

I would challenge Dr. Caruncho to identify an article opposing screening prior to age 50 that clearly stated that age 50 is an “arbitrary” threshold. If women had been told that they were being denied access to screening, arbitrarily, until age 50, despite the fact that screening could decrease deaths while they were in their 40s, I suspect there would have been a discussion. Instead they were told the trials showed no benefit, so that the discussion was avoided.

The CNBSS1 was a completely corrupted trial. It was underpowered6 with poor quality mammography.7 It violated the most fundamental requirement of a randomized trial: blinded randomization. They examined everyone so that they knew who had advanced cancers before allocation. They then assigned women on open lists so that a line could be skipped to insure that a woman with advanced cancer would be placed in the mammography group. It is clear that this occurred and biased the trial.8 It is incredible that anyone who understands RCT continues to defend the CNBSS1.

Did Dr. Caruncho wonder why Berry (and the U.S. Preventive Services Task Force) chose computer models when there are direct data from the Netherlands9 and Sweden10-12 showing that the vast majority of the decrease in deaths is due to screening, with only a small component due to improved therapies, and that screening the general public reduces breast cancer deaths by over 30% (including women in their 40s), not the 15% used by the USPSTF? Models are only as good as the assumptions programmed into the computer and the assumptions determine the results. Therapy is successful at saving lives only when breast cancers are found early. I didn't think I had to point this out, but the only way to detect cancer early, with proven mortality reduction, is with mammography screening.

The U.S. death rate from breast cancer has decreased by 30% since 1990. This amounts to 15,000 to 20,000 lives that are being saved each year primarily due to mammography screening. Dr. Caruncho feels this is trivial. I do not. The scientific evidence clearly shows that mammography screening, beginning by the age of 40, significantly reduces breast cancer deaths.

Daniel B. Kopans, M.D.
Professor of radiology, Harvard Medical School
Senior Radiologist, Breast Imaging Division
Department of Radiology,
Avon Comprehensive Breast Evaluation Center
Boston, MA

References

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5. Kopans DB, Moore RH, McCarthy KA, et al. Biasing the interpretation of mammography screening data by age grouping: nothing changes abruptly at age 50. Breast J 1998;4():139-145.
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