Reflections on Screening Mammography and the Early Detection of Breast Cancer

Abstract

A Countercurrents Series a with S.A. Narod md assigned surreptitiously to the mammography arm, which explains the lack of observed benefit 11 .The most recent nbss report 1 tallied the breast cancers that occurred in each of the two study arms after the screening period ended (that is, between years 6 and 25), counting 2584 cancers in the screening arm and 2609 cancers in the control arm. If the screening arm had been enriched for women at "high risk," that enrichment must have been performed in a peculiar fashion, using only risk factors that have a transient effect. Perhaps Dr. Mukherjee would care to explain what those factors were. It follows that the excess of cancers seen in the screening period (years 1-5: 666 vs. 524) was a result of early diagnosis and not from stacking the deck.In any case, compelling evidence against the criticism of assignment of high-risk women to the screening arm is provided in the most recent analysis 1 , and that criticism is no longer raised (although no one has retracted or apologized). Instead, critics now insist that many women with palpable lesions were sent directly to the screening arm by duplicitous research assistants. There is no reason to believe that such actions (which would involve a national conspiracy of dozens of coordinators who spoke two official languages) were taken, but even if they had been, the study and its conclusions would not necessarily be invalidated. Even if all the women with prevalent cancers had been shunted to the screening arm, the situation could still be remedied by ignoring all cancers found at the first screening round (prevalent cancers) and focusing instead on the incident cancers. Such a strategy is not uncommon in screening studies. In the nbss, no woman had the opportunity to "cross the floor" from one study arm to the other after initial assignment. Therefore, if we exclude all prevalent cases from the analysis and focus on women with no cancer at study entry, we can re-evaluate the benefit of mammography thereafter. The hazard ratio for death from breast cancers detected in screening rounds 2-5 was 0.90 (95% confidence interval: 0.69 to 1.16; p = 0.40).A little learning is a dangerous thing. -Alexander Pope, An Essay on CriticismIn the stormy aftermath of the recent publication of results from the 25-year Canadian National Breast Screening Study (nbss) 1 , various opinions questioning the validity of the study's results have been expressed 2-7 . I was a latecomer to the study. In 2005, I was charged with oversight of the final record linkage and the statistical analysis and interpretation of the final data set. Dr. Anthony Miller has been my mentor since 1987. Our first joint paper, on screening for cervical cancer, was published in 1991 8 . I chose not to respond to individual criticisms, but instead to collect my thoughts and to try to explain why the study authors saw no benefit from screening.Most of the criticism from the radiology community focuses on issues of study design (which they claim was inadequate) and on the quality ...

Global patterns and trends in the breast cancer incidence and mortality according to sociodemographic indices: an observational study based on the global burden of diseases

“…In many LMICs, the burdens of infection-related cancers, including cervical, gastric and liver cancer, remained higher than those of breast cancer 1 2. Moreover, high-income countries have generally implemented mammographic screening programmes, especially for women aged 50–69 years 25–27. Consistently, our age-based subgroup analysis confirmed a transient increase in the incidence of breast cancer among women aged 50–69 years and a subsequent decrease among those aged 70+ years in countries with high SDI values.…”

Cancer screening in the United States, 2015: A review of current American Cancer Society guidelines and current issues in cancer screening

“…Given the enduring challenges to the value of mammography, the response to the results has been contentious, with some asserting that the CNBSS results are definitive evidence that early diagnosis of breast cancer has little value, and others arguing that methodological and protocol decisions largely explain the counterintuitive findings …”

“…49 At 25 years of follow-up, the investigators combined the 2 study groups into a single evaluation group, and consistent with earlier evaluations, did not observe a lower breast cancer death rate in the groups invited to mammography screening compared with the control group (hazard ratio, 0.99; 95% confidence interval, 0.88-1.12). 44 Given the enduring challenges to the value of mammography, the response to the results has been contentious, with some asserting that the CNBSS results are definitive evidence that early diagnosis of breast cancer has little value, 50,51 and others arguing that methodological and protocol decisions largely explain the counterintuitive findings. [52][53][54] How do we understand these findings, which are at variance with the other breast cancer screening randomized trials?…”

Point: Mammography Screening—Sticking to the Science

“…In his November 2014 article 9 , Dr. Steven Narod defended the cnbss, which has been heavily criticized by other scientists on the basis of methodologic flaws and poor mammography quality [10][11][12] .…”