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The Effect of Mammographic Screening and Hormone Replacement Therapy Use on Breast Cancer Incidence in England and Wales

¹ Cancer Screening Evaluation Unit, Institute of Cancer Research, Sutton, United Kingdom; ² Cancer Research UK Epidemiology Unit, Nuffield Department of Clinical Medicine, University of Oxford, Oxford, United Kingdom; and ³ Thames Cancer Registry, King's College London, London, United Kingdom

Requests for reprints: Henrik Møller, Thames Cancer Registry, King's College London, London SE1 3QD, United Kingdom. E-mail: henrik.moller{at}kcl.ac.uk

Design: An extended age-period-cohort model was used to estimate the effect of mammographic screening and hormone replacement therapy on breast cancer incidence in England and Wales between 1971 and 2001.

Results: Incidence of breast cancer increased noticeably in women attending screening for the first time compared with nonattenders [rate ratio (RR), 1.73; 95% confidence interval (95% CI), 1.67-1.80]. Incidence was also 18% to 35% higher in attenders relative to nonattenders in subsequent screening rounds. In the first 3 years after women left the screening program, rates of breast cancer were reduced (RR, 0.88; 95% CI, 0.86-0.90), but by 7 to 9 years after screening, the rates had returned to the expected level (RR, 0.97; 95% CI, 0.94-1.00). The estimated RR of hormone replacement therapy on breast cancer incidence was 1.55 (95% CI, 1.37-1.75). Screening is estimated to increase a woman's lifetime risk of being diagnosed with breast cancer from 7.8% to 8.6%.

Conclusions: It is estimated that in the absence of screening, rates of breast cancer incidence would have continued to increase. A study at the individual subject level would be beneficial to assess the level of overdiagnosis associated with breast cancer screening. (Cancer Epidemiol Biomarkers Prev 2007;16(11):2257–61)