Mammogram Controversy … Or Is It?
Once again, the controversy regarding the benefit of routine screening mammogram has been pushed to center stage. Unfortunately, doubt about the value of mammography ripped through the media before serious doubts about the validity of last week’s Canadian National Breast Screening Study (British Journal of Medicine) were properly investigated. In an environment when unsubstantiated fears about the risks of mammography and claims of ‘overtreatment’ of some cancers, this misleading and poorly constructed study, continues to fuel these fears, and, unfortunately, will very likely lead some to avoid this potentially lifesaving screening tool.
Here are a few of the serious concerns about this study:
- Although reported as a 25 year study, this is actually a study of 5 years of poor quality mammography with a subsequent long follow-up period.
- The Canadian control group was not standard of care. In the trial the control group had regular breast exams by highly trained and experienced nurses. Thus the average size of cancers in the control group was similar to the size of screen detected cancers. This would never happen in the real world and did not happen in any other randomized trial where standard of care was routine clinical care and the size of cancers in the control group was much greater than in the screened group.
- There are serious signs of “contamination” of the mammography arm, resulting from improper randomization at the beginning of the study. Evidence for this: the higher than expected number of women with palpable masses (68%) and large mean tumor size (1.9 cm) in the mammogram arm, compared to the physical exam only arm.
- The authors claimed that 22% of the invasive cancers detected were over diagnosed, meaning non-lethal cancers that could have been left alone and undetected. This claim represents a pure assumption. Do people really believe the misleading information that new treatments render early detection unnecessary as Drs. Kalager and Miller wants you to believe? The facts clear the issue: follow-up of 9040 patients with breast cancers diagnosed between 1998–2003 showed that even in the era of adjuvant systemic therapy, node-negative cancers still have considerably better survival than node positive. While survival of women with node-positive tumors has improved in the era of adjuvant systemic therapy compared with earlier times, it clearly is a worthy goal to have the cancer diagnosed before it spreads to the lymph nodes. Screen detected node positive cases had a better survival than clinically detected node negative cases. Thus, improvements in therapy have not rendered early detection redundant. (Tabar)
- We have proof from more rigorous studies of a significant survival benefit that’s attributable to mammography: Swedish Two-County trial (Tabar et al.: Radiology, 2011, Vol.260: 658-663).
With permission, here is a letter sent to the studies author, by Drs.. Tabar and Linver (authors of the Sweedish Two County Trial):
Good evening Tony,
We are thoroughly shocked by your recent article published in the BMJ. In the intervening years since your original publication in 1990, there have been so much documented data published within the scientific community of your faulty trial design and manipulative execution that it is clear to the critical and ethical portion of the scientific world that the NCBSS should have been terminated long before it even began, and should certainly be given no credence in any decision-making in regards to the value of screening mammography. Your study is such an embarrassment to the scientific world that your attempt to compare it with the Swedish Two-county Trial borders on obscenity. We have attached some comments from colleagues around the world, some of the most embarrassing from Canada.
Michael Linver, MD, FACR.
Laszlo Tabar, MD, FACR (Hon)
In addition, here their letters to the editor of the NY Times:
Laszlo Tabar, M.D.,F.A.C.R. (Hon) Sweden :
We do not want to go back to the Dark Ages. The Canadian trials were a failure from the beginning: they used substandard and outdated mammography technique to claim that mammography screening would add nothing beyond what physical examination can accomplish; they were not population based; they could not evaluate the independent impact of mammography due to the confounding effect of physical examination. Therefore these trials were excluded from the meta-analysis by the WHO’s (World Health Organization) workshop in 2002, even though AB Miller chaired the section. Three authors of the current article have agreed with the conclusion of the WHO publication: “There is sufficient evidence for the efficacy of screening women aged 50-69 years by mammography as the sole screening modality in reducing mortality from breast cancer”. Nevertheless, twelve years later they revert to their earlier opinion that mammography does not have an effect on mortality from breast cancer. The current BMJ article does not provide news for anyone, since these trials have been plagued with serious quality assurance problems that have been well known and carefully documented over the past few decades. Dr. Boyd’ conclusion published 21 years ago is still valid: “the results of these trials should not be used to change the prevailing scientific view of the potential benefits of screening with mammography.”
Michael Linver, M.D., F.A.C.R. :
Congratulations on your latest contribution to the premature deaths and unnecessary suffering of untold numbers of young women who will contract breast cancer in the next few years. Your biased and one-sided coverage of the 25 year results of the Canadian breast screening trial gives undeserved credence to one of the only randomized controlled trials (of at least 10 others) to show no benefit in decreasing deaths from breast cancer. The Canadian trial is our very best example of how bad mammography is worse than no mammography at all, and has been criticized by scientists around the world for its poor design and highly questionable results. It is truly “garbage in, garbage out”. Why you have not given equal coverage to the multitude of even larger studies by Tabar and others showing as much as a 63% decrease in breast cancer deaths in women screened with mammography is very disturbing to me. You will clearly convince many unsuspecting and less knowledgeable women to forego mammography, and lose their only chance of surviving this terrible disease. The consequent blood on your hands will likely never wash out.