Letter to the Editor: Hofvind S, Skaane P. Stage distribution of breast cancer diagnosed before and after implementation of population-based mammographic screening. Fortschr Röntgenstr 2012; 184: 437–442

Letter to the Editor

Dear Editor,

I read with interest the article published by Hofvind and Skaane [1]. After 17 years of breast cancer screening in Norway, Hofvind and Skaane still focus on stage distribution as a surrogate of the benefit of mammography screening instead of focusing on the only reliable outcome; mortality from breast cancer. Sadly, their use of stage distribution as the percentage of detected tumors is biased. It seems as there is a real stage shift among screened (Table 2), with 1.3 % of all tumors in stage III and IV. However, use of percentage is misleading in this context, as it includes overdiagnosed cases of breast cancers in the denominator. A much more valid approach is to use incidence rates (where the denominator are number of women-years), not percentages. Incidence rates for stage III and IV breast cancer in the Norwegian Breast Cancer Screening Program were similar for women invited to screening compared to women not invited [2].

Further, the authors state that our study published in the New England Journal of Medicine (NEJM) “has been heavily criticized due to methodological issues”. However, they failed to mention that these “issues” have been clarified and dismissed as unjustified [3]. In fact, the data presented by Hofvind and Skaane fit perfectly with what we observed in our New England Journal paper; their Fig. 2 shows a 35 % reduction of breast cancer mortality in the pilot counties, and a 26 % reduction in the nonpilot counties. This corresponds perfectly with the 10 % nonsignificant reduction in mortality that we observed [4]. Further, as Fig. 2 clearly shows, the decline in breast cancer mortality started before the mammography screening program was introduced. Only a small fraction of the reduction in mortality seen in the nonpilot counties could be associated with the screening program, and not the whole reduction seen in the pilot counties could be associated with the screening program. Thus, the study by Hofvind and Skaane confirms our findings published in NEJM [4].

M. Kalager, University of Oslo, Institute of Health and Society, Department of Health Management and Health Economics and Telemark Hospital and Harvard School of Public Health, Department of Epidemiology, P. O. Box 1089 Blindern, 0318 Oslo, Norway

• References

• 1 Hofvind S, Skaane P. Stage distribution of breast cancer diagnosed before and after implementation of population-based mammographic screening. Fortschr Röntgenstr 2012; 184: 437-442
• 2 Kalager M, Adami HO, Bretthauer M et al. Overdiagnosis of invasive breast cancer due to mammography screening: results from the Norwegian screening program. Ann Intern Med 2012; 156: 491-499
• 3 Kalager M, Zelen M, Adami HO. More on screening mammography. Authors reply. N Engl J Med 2011; 364: 285
• 4 Kalager M, Zelen M, Langmark F et al. Effect of screening mammography on breast-cancer mortality in Norway. N Engl J Med 2010; 363: 1203-1210
• 5 Hofvind S, Lee CI, Elmore JG. Stage-Specific Breast Cancer Incidence Rates Among Participants and Non-Participants of a Population-Based Mammographic Screening Program. Submitted for publication.
• 6 Hofvind S, Sakshaug S, Ursin G et al. Breast cancer incidence trends in Norway – explained by hormone therapy or mammographic screening?. Int J Cancer 2012; 130: 2930-2938