Calculating appropriate target cancer detection rates and expected interval cancer rates for the UK NHS Breast Screening Programme. Interval Cancer Working Group.

OBJECTIVES: To enable better monitoring of interim outcome measures in the NHS Breast Screening Programme by providing revised targets for cancer detection rates, and revised expected interval cancer rates. DESIGN AND SETTING: Expected detection rates of invasive cancers at prevalent screen are calculated, using estimates of the underlying England and Wales incidence rates and age specific prevalence incidence ratios from the Swedish Two County Study. Expected interval cancer rates are also derived from this study, and are used to calculate expected detection rates at rescreening. RESULTS: The expected invasive cancer detection rates at first screen for women aged 50-52 is 3.6 per 1000. The expected rate at rescreening for women aged 53-64 is 4.0 per 1000. Expected interval cancer rates for women screened from 1995/6 onwards are 0.45 per 1000, 0.65 per 1000, and 1.2-1.3 per 1000 for the periods within 0-<12, 12-<24, and 24-<36 months of screening. CONCLUSIONS: The target cancer detection rates and expected interval cancer rates for the NHS Breast Screening Programme have been revised in the light of more recent data. Monitoring of the extent to which the programme is meeting these revised targets will give a more accurate indication of the potential to meet the Health of the Nation target of a 25% reduction in breast cancer mortality by the year 2000.