by Constantine Kaniklidis *, Research Director, No Surrender Breast Cancer Foundation (NSBCF) **
Understanding – and Measuring – Overdiagnosis Overdiagnosis occurs when the patient, were it not for screening, would have died of some other non-cancer cause without ever having been diagnosed with malignancy. Overdiagnosis estimates are fraught with many complex limitations and challenges, but overdiagnosis estimates can be “normalized” by drawing on only studies restricted to actual screening-attendant women (as opposed to only screening-invited women) and which also control for the major known confounding factors. The EUROSCREEN review (2 million women age 50 or older in 18 countries) which met these requirements found overdiagnosis as being just 6.5%, and autopsy studies find only a small degree of overdiagnosis (under 10% total, just 1.3% for invasive breast cancers only).
The Price of Underdiagnosis Against overdiagnosis, there are real harms to underdiagnosis. Survival declines for each annual mammography screening a women elects to omit: a women missing any of their previous five annual screenings more than doubles her risk of death compared with not missing any.
What About DCIS? A central issue in the mammography debate as it concerns overdiagnosis surrounds ductal carcinoma in situ (DCIS), a non-invasive condition – but with a non-trivial potential to become invasive – marked by the presence of abnormal cells inside a milk duct in the breast. It is argued by some that if mammography screening detects, as it appears to, high proportions of, or primarily, DCIS (and other lesions of minimal potential to advance invasive cancers), then regardless of the benefits of screening, the harms of detecting non-threatening lesions would outweigh the benefits, as many women could be subjected to unnecessary further diagnostic procedures, or possibly treatments, for conditions that would in all probability not advance to significantly compromise their survival.
So what do we know? It appears that more than half of all mammographically detected DCIS are in fact high grade, which means they have a high risk of progression. And it appears that most screening-detected cases of DCIS have in fact significant invasivity potential (being medium and high grade), and this in turn strongly suggests, against screening critics, that the observed high detection of DCIS by screening mammography cannot continue to be construed as a real harm. For screening advocates it attests to screening “doing its job”.
What Do Women Really Think? Women overwhelmingly elect annual mammographic screening, and even when informed of potential harms, women prefer the risk of overtreatment to the risk of undertreatment, a decision posture I call regret minimization.
Lessons Learned So despite the possibility of a non-trivial degree of overdiagnosis from mammography screening, the best evidence suggests that the level is small and unlikely to exceed 10%, and that the balance of benefits and harms still weighs in on the side of the positive value mammography screening.
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.
* Constantine Kaniklidis is currently Director of Research for the No Surrender Breast Cancer Foundation (NSBCF), a not-for-profit organization providing high-quality critically reviewed and appraised information and guidance to the breast cancer community. His focus is on the most challenging of advanced / metastatic disease, especially triple negative breast cancer (TNBC) and inflammatory breast cancer (IBC). He is also the Editor of Evidence-based Medicine for the Open Directory Project. Research interests include epigenetic reprogramming, optimal treatment of CNS metastases (brain and leptomeningeal), drug interactions and resistance in oncology, and evidence-based integrative oncology. He is also active at the intersection of politics and medicine, as in his widely accessed paper “Cancer, Culture and Cooperation in the Middle East”.
** The No Surrender Breast Cancer Foundation is a U.S.-based 501(c)3 not-for-profit organization.