1. ¹Cancer Screening Evaluation Unit, Institute of Cancer Research, Brookes Lawley Building, 15 Cotswold Road, Sutton, Surrey SM2 5NG, UK
2. ²Department of Pathology, Western General Hospital, Crewe Road, Edinburgh EH4 2XU, UK
3. ³Department of Reproductive Epidemiology, University of Leeds, Leeds Screening Centre, 3 Gemini Park, Sheepscar Way, Leeds LS7 3JB, UK

Correspondence: Dr S Moss, E-mail: sue.moss@icr.ac.uk

⁴Professor H Cuckle (Chair), Professor TJ Anderson, Dr M Cohen, Dr A Evans, Ms J Hayes, Dr E Kutt, Dr SM Moss, Dr B Muir, Dr C Record, Dr BA Thomas, Ms I Thomas (Trial Co-ordinator)

Received 24 September 2004; Revised 13 December 2004; Accepted 15 December 2004; Published online 22 February 2005.

Abstract

A trial in the UK to study the effect on mortality from breast cancer of invitation for annual mammography from the age of 40–41, has randomised a total of 160 921 women in the ratio 1 : 2 to the intervention and control arms. All breast cancers diagnosed in the two arms have been identified, and the histology reviewed. This paper presents the results of an interim analysis using surrogate outcome measures to compare predicted breast cancer mortality in the two arms based on 1287 cases diagnosed to 31.12.1999. Due to earlier diagnosis, there is currently an 8% excess of invasive breast cancers in the intervention arm. The ratio of predicted deaths at 10 years in the intervention arm relative to the control arm, adjusted for this excess diagnosis, ranges from 0.89 (95% confidence interval (CI) 0.78–1.01) to 0.90 (95% CI 0.80–1.01). Screening from age 40 may result in a lower reduction in breast cancer mortality than that observed in other trials including women below age 50. This analysis based on surrogate outcome measures suggests that a reduction in breast cancer mortality may be observed in this trial. However, a number of assumptions have been necessary and firm conclusions must await the analysis of observed mortality from breast cancer.