by Anthony B. Miller, MD, FRCP. Professor Emeritus, Dalla Lana School of Public Health, University of Toronto
When the 25-year report of the Canadian National Breast Screening Study (CNBSS) was published , showing no benefit from mammography screening, there was much dissension, and attempts to show that what we reported could not be true [2,3], to which we responded . The belief that “early” detection of a cancer is bound to be beneficial is entrenched in our society, people do not understand that the mere early detection of a cancer does not automatically result in benefit, the cancer may not have been destined to be fatal with modern therapy even when detected later by the woman herself, the cancer might never have progressed to become detectable by the woman if it had not been revealed by the mammogram, or, the cancer was destined to kill whatever stage it was detected because of its innate biology. Even if we accept that mammography screening reduces breast cancer mortality by 15-20% , and I do not, that means that 80% or more of the deaths from breast cancer destined to occur will still do so.
But there are wider implications of our study. If mammography screening does not have the expected effect, and the recent Danish study confirms this , how can we reduce the toll of breast cancer? The first priority is to recognize that we can do something to prevent breast cancer by means of actions well-recognized to promote health: physical exercise, a healthy diet with plenty of fruits and vegetables, avoidance of obesity after the menopause, avoiding prolonged use of hormonal replacement therapy, not smoking, and drinking alcohol in moderation (not more than one drink a day), actions that should start early in life and continue throughout life . Further, women should understand that if they plan to have children the first child should preferably be born under her age of 25, though if the woman’s first birth is delayed to age 30 or more, the child should be breast fed for at least 5 months to reduce the woman’s risk of breast cancer . The second is to promote early cancer diagnosis , by what in the West we now term “breast awareness”: encouraging women to be aware of the appearance and feel of their breasts, and if she detects an abnormality in her breast to seek skilled examination by physicians who know the signs of early breast cancer, followed by appropriate diagnostic tests – diagnostic mammography and/or ultrasound. And if breast cancer is confirmed, prompt breast-conserving surgery and adjuvant chemotherapy or hormone therapy if deemed necessary.
Despite claims to the contrary, there is no reason to believe that more modern forms of mammography than were used in the CNBSS, or other more “sensitive” screening tests, will improve the situation – all they are likely to do is to increase the overdiagnosis of breast cancer, the detection of a cancer not destined to progress and kill in the woman’s lifetime . Successful screening for cervix and colorectal cancer depends on the detectability and effective treatment of a cancer precursor. Such a precursor has not yet been identified for breast cancer; ductal carcinoma in situ is not an obligate breast cancer precursor . It is high time we recognized that breast screening is not the panacea it is cracked up to be, and concentrate on more appropriate forms of breast cancer control, especially prevention.
Click here to read the Table of Contents for the series: Breast Cancer Screening, Mammography and “Alternative Facts”
The opinions expressed in this article are the author’s own and do not reflect the view of Cancer Knowledge Network or Multimed Inc.
- Miller AB, Wall C, Baines CJ, Sun P, To T, Narod SA. Twenty five year follow-up for breast cancer incidence and mortality of the Canadian National Breast Screening Study: randomised screening trial. BMJ 2014;348:g366.
- Kopans D; 2014. http://www.bmj.com/content/348/bmj.g366?tab=responses
- Tabár L; 2014. http://www.bmj.com/content/348/bmj.g366?tab=responses
- Miller AB, Wall C, Baines CJ, Sun P, To T, Narod SA; 2014. http://www.bmj.com/content/348/bmj.g366?tab=responses
- Independent UK Panel on Breast Cancer Screening. The benefits and harms of breast cancer screening: an independent review.Lancet 2012; 380:1778-1786.
- Jørgensen KJ, MD, Gøtzsche PC, Kalager M, Zahl P-H. Breast Cancer Screening in Denmark: A Cohort Study of Tumor Size and Overdiagnosis. Ann Intern Med. 10 January 2017. DOI: 10.7326/M16-0270
- Miller AB. What Causes Cancer? What we know and what it means. Victoria BC, Friesen Press, 2014. (http://www.friesenpress.com/bookstore/title/119734000012176596).
- Chang-Claude J, Eby N, Kiechle M, Bastert G, Becher H. Breastfeeding and breast cancer risk by age 50 among women in Germany. Cancer Causes and Control 2000; 11: 687-695.
- WHO Guide to Early Cancer Diagnosis. Geneva, World Health Organization, 2017.
- Baines CJ, To T, Miller AB. Revised estimates of overdiagnosis from the Canadian National Breast Screening Study. Preventive Medicine 2016; 90: 66–71.
- To T, Wall C, Baines CJ, Miller AB. Is carcinoma in situ a precursor lesion of invasive breast cancer? Int. J. Cancer 2014; 135: 1646–1652.
Anthony B. Miller, MD, FRCP, FRCP(C), FACE is Professor Emeritus in the Dalla Lana School of Public Health, University of Toronto, Canada, and Director of the Canadian National Breast Screening Study. After training in internal medicine in the UK, he was a member of the scientific staff of the Medical Research Council’s Tuberculosis and Chest Diseases Unit 1962-71. He was Director of the Epidemiology Unit of the National Cancer Institute of Canada, 1971-86 and Chairman of the Department of Preventive Medicine and Biostatistics, University of Toronto, 1992-6. He served as Special Expert in the Early Detection Branch, Division of Cancer Prevention, US National Cancer Institute, 1996-7, Senior Epidemiologist, International Agency for Research on Cancer, Lyon, France 1997-8, Head, Division of Clinical Epidemiology, Deutsches Krebsforschungszentrum, Heidelberg, Germany 1998-2002, Associate Director, Research, Dalla Lana School of Public Health, University of Toronto, January 2009-December, 2010 and Visiting Senior Scientist, International Agency for Research on Cancer, Lyon, France, September 2011-January 2012. He has been a consultant to the World Health Organization (WHO) on Cancer Control and Special Advisor to the Eastern Mediterranean Region of WHO on Early Detection and Cancer Control. He is Scientific Lead of the OncoSim Initiative of the Canadian Partnership against Cancer and a member of the Partnership’s Cancer Control Council.