We are dismayed by the report on breast self-examination by Nancy Baxter and colleagues.1 Our detailed response is available as an eLetter at www.cma.ca/cmaj/eLetterAdmin/view.asp?id=42. Here we summarize our main points.
The report only refers to the St. Petersburg component of the Russia – World Health Organization trial of breast self-examination. The Moscow component comprises 74 378 women recruited in 272 clusters, whereas the St. Petersburg component has 28 clusters.2 None of the reports that have appeared to date on the St. Petersburg component have taken note of the cluster randomization, which is necessary for statistical validity. Further, there was concurrent screening in St. Petersburg, where breast self-examination is being evaluated in terms of what it adds to routine annual physical examinations. The investigators in both centres are arranging for the transfer of data to a centre approved by the World Health Organization for a definitive analysis. Until that analysis has been performed, any inferences based on the trial are premature.
In our nested case–control study of breast self-examination we had planned exploratory analyses at the time the study was initiated.3 Further, we were able to adjust for differences in risk factors between cases and controls. Thus, we disagree with the comments on this study in Table 2 of the report by Baxter and colleagues.1 Although there may be residual selection bias, this is precisely the reason why case–control studies are categorized as level II-2 evidence rather than level I evidence. A similar comment relates to the cohort study of people who complied with breast self- examination in Finland.4 Thus, these 2 studies, both of which showed a significant effect of good compliance with breast self-examination in reducing breast cancer mortality, justify an upgrading from a grade C to a grade B recommendation.
We conclude that in the context of Canadian screening programmes with screening every 2 years, women should be taught breast self-examination. If breast self-examination is practised well and physicians are aware of the signs of early breast cancer, breast self-examination helps to reduce breast cancer mortality.
Signatures
Anthony B. Miller
Division of Clinical Epidemiology Deutsches Krebsforschungszentrum Heidelberg, Germany
Cornelia Baines
Department of Public Health Sciences University of Toronto Toronto, Ont.
Bart Harvey
Department of Public Health Sciences University of Toronto Toronto, Ont.
References
- 1.Baxter N, with the Canadian Task Force on Preventive Health Care. Preventive health care, 2001 update: Should women be routinely taught breast self-examination to screen for breast cancer? CMAJ 2001;164(13):1837-46. [PMC free article] [PubMed]
- 2.Semiglazov VF, Sagaidack VN, Moiseyenko VM, Mikhailov EA, for the Russian Federation World Health Organization Study. Study of the role of breast self-examination in the reduction of mortality from breast cancer. Eur J Cancer 1993; 29A:2039-46. [PubMed]
- 3.Harvey BJ, Miller AB, Baines CJ, Corey PN. Effect of breast self-examination techniques on the risk of death from breast cancer. CMAJ 1997; 157(9):1205-12. [PMC free article] [PubMed]
- 4.Gastrin G, Miller AB, To T, Aronson KJ, Wall C, Hakama M, et al. Incidence and mortality from breast cancer in the Mama program for breast screening in Finland, 1973–1986. Cancer 1994; 73:2168-74. [DOI] [PubMed]