It is disheartening to write this response to our own Academic Radiology . The commentary using the misnomer “Mammogram Trials” by Jha and Ware describes only a single trial—the outlier—the only randomized controlled study published that did not show a mortality benefit from screening mammography. Although experts in breast cancer and breast imaging would disagree with much of the article, the issue of overdiagnosis raised by Jha and Ware requires clarification.
Overdiagnosis is the detection of a breast cancer that would not have otherwise surfaced in a woman’s lifetime and would not have threatened her life . Jha and Ware state that based on the Canadian National Breast Screening Study, the overdiagnosis rate for mammography is at least 20%. Even if the results of the Canadian National Breast Screening Study were to be taken seriously (the study is so strikingly flawed that many experts argue the results are entirely invalid), the study’s data itself actually show an overdiagnosis rate less than 5%. This lower estimate is in keeping with other randomized controlled trials and a review of 13 European observational studies, all of which found overdiagnosis estimates in the range of <1–10% . The complexities of the issue, including incorporation of baseline breast cancer incidence trends and lead time, are entirely ignored by Jha and Ware.
Although overdiagnosis is an important conceptual problem, the reality is that in the current medical paradigm, even at the height of our scientific understanding, we cannot determine which identified cancers will progress to be potentially life threatening and which will remain harmless. Hence, although an easy attack point for critics of mammography, the concept of overdiagnosis becomes extremely difficult to operationalize. To use Drs. Jha and Ware’s chosen Latin dictum—reductio ad absurdum—if overdiagnosis is such a concern, there should be no diagnosis of any breast cancer at all because some cancers will be harmless and those women are being overdiagnosed and overtreated. The idea is simply ridiculous. Until we can prospectively determine which lesions are potentially fatal and which are indolent, lesions need to be identified and treated. To do otherwise is to gamble with women’s lives. To take the best possible care of our patients, we need to continue to find breast cancer early, while it is most treatable, even curable. Screening mammography remains the best way to do this. Like all of medicine, mammography is not perfect, but robust science has shown mammography saves lives . This is what needs to be emphasized.
References
1. Jha S., Ware J.B.: Mammogram trials. Acad. Radiol 2015; 22: pp. 973-975.
2. Miller A.B., Wall C., Baines C.J., et. al.: 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
3. International Agency for Research on Cancer Handbook on Cancer Prevention 2002; 7: pp. 144.
4. Zackrisson S., Andersson I., Janzon L., et. al.: Rate of over-diagnosis of breast cancer 15 years after end of Malmo mammographic screening trial: follow-up study. BMJ 2006; 332: pp. 689-692.
5. Duffy S.W., Agbaje O., Tabar L., et. al.: Overdiagnosis and overtreatment of breast cancer: estimates of overdiagnosis from two trials of mammographic screening for breast cancer. Breast Cancer Res 2005; 7: pp. 258-265.
6. Puliti D., Duffy S.W., Miccinesi G., et. al.: Overdiagnosis in mammographic screening for breast cancer in Europe: a literature review. J Med Screen 2012; 19: pp. 42-56.
7. Tabar L., Vitak B., Chen T.H., et. al.: Swedish two-county trial: impact of mammographic screening on breast cancer mortality during 3 decades. Radiology 2011; 260: pp. 658-663.
8. Smith R.A., Duffy S.W., Gabe R., et. al.: The randomized trials of breast cancer screening: what have we learned?. Radiol Clin North Am 2004; 42: pp. 793-806.