Published in:
Open Access 01-12-2012 | Research article
Modelling the overdiagnosis of breast cancer due to mammography screening in womenaged 40 to 49 in the United Kingdom
Published in: Breast Cancer Research | Issue 6/2012
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Introduction
Overdiagnosis of breast cancer due to mammography screening, defined as thediagnosis of screen-detected cancers that would not have presented clinically in awomen's lifetime in the absence of screening, has emerged as a highly contentiousissue, as harm caused may question the benefit of mammographic screening. Moststudies included women over 50 years old and little information is available foryounger women.
Methods
We estimated the overdiagnosis of breast cancer due to screening in women aged 40to 49 years using data from a randomised trial of annual mammographic screeningstarting at age 40 conducted in the UK. A six-state Markov model was constructedto estimate the sensitivity of mammography for invasive and in situ breast cancer and the screen-detectable mean sojourn time fornon-progressive in situ, progressive in situ, and invasivebreast cancer. Then, a 10-state simulation model of cancer progression, screening,and death, was developed to estimate overdiagnosis attributable to screening.
Results
The sensitivity of mammography for invasive and in situ breast cancerswas 90% (95% CI, 72 to 99) and 82% (43 to 99), respectively. The screen-detectablemean sojourn time of preclinical non-progressive and progressive in situ cancers was 1.3 (0.4 to 3.4) and 0.11 (0.05 to 0.19) years, respectively, and0.8 years (0.6 to 1.2) for preclinical invasive breast cancer. The proportion ofscreen-detected in situ cancers that were non-progressive was 55% (25 to77) for the first and 40% (22 to 60) for subsequent screens. In our main analysis,overdiagnosis was estimated as 0.7% of screen-detected cancers. A sensitivityanalysis, covering a wide range of alternative scenarios, yielded a range of 0.5%to 2.9%.
Conclusion
Although a high proportion of screen-detected in situ cancers werenon-progressive, a majority of these would have presented clinically in theabsence of screening. The extent of overdiagnosis due to screening in women aged40 to 49 was small. Results also suggest annual screening is most suitable forwomen aged 40 to 49 in the United Kingdom due to short cancer sojourn times.