CALCULATING APPROPRIATE TARGET CANCER-DETECTION RATES AND EXPECTED INTERVAL CANCER RATES FOR THE UK NHS BREAST SCREENING-PROGRAM

Objectives-To enable better monitoring of interim outcome measures in the NHS Breast Screening Programme by providing revised targets for ca ncer detection rates, and revised expected interval cancer rates. Desi gn and setting-Expected detection rates of invasive cancers at prevale nt screen are calculated, using estimates of the underlying England an d 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 detec tion rates at rescreening. Results-The expected invasive cancer detect ion rates at first screen for women aged 50-52 is 3.6 per 1000. The ex pected rate at rescreening for women aged 53-64 is 4.0 per 1000. Expec ted 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 with in 0-<12, 12-<24, and 24-<36 months of screening. Conclusions-The targ et cancer detection rates and expected interval cancer rates for the N HS Breast Screening Programme have been revised in the light of more r ecent data. Monitoring of the extent to which the programme is meeting these revised targets will give a more accurate indication of the pot ential to meet the Health of the Nation target of a 25% reduction in b reast cancer mortality by the year 2000.