Screening histories of invasive breast cancers diagnosed 1989-2006 in the West Midlands, UK: variation with time and impact on 10-year survival.

OBJECTIVES: To examine variations in screening status category with time for 20,862 invasive breast cancers diagnosed in the West Midlands between 1989 and 2006, and to provide 10-year relative survival rates for each category.
METHOD: Population-based breast screening was introduced in the West Midlands from 1988. Primary invasive breast cancers diagnosed from 1 April 1989 to 31 March 2006 in women eligible for breast screening were identified from the West Midlands Cancer Intelligence Unit's cancer registration database. A screening status was determined for each case using previously published methodology.
RESULTS: Screening status rates are affected initially by the gradual rollout of the screening programme and more recently by the need to wait for three years before interval cancers and cancers in lapsed and non-attenders can be identified. In the steady-state period 1994-2003, 40.6% of invasive breast cancers were screen-detected, 36.3% were interval cancers and 11.2% were cancers in non-attenders (NA). Ten-year relative survival was 89.6% for screen-detected breast cancers, 73.3% for interval cancers and 51.9% for cancers in NA.
CONCLUSION: The detection of invasive breast cancers by screening has improved over time, with an equivalent reduction in the numbers of interval cancers. This, together with a stable rate of cancers in NA and an improvement in the survival of women with interval cancers, suggests that further improvements in breast cancer mortality can be predicted. International comparisons of interval cancer rates are difficult due to interprogramme differences in the time between screens.