Proportional incidence and radiological review of large (T2+) breast cancers as surrogate indicators of screening programme performance.

Objectives: Surrogate measures of screening performance [e.g. interval cancer (IC) proportional incidence] allow timely monitoring of sensitivity and quality. This study explored measures using large (T2+) breast cancers as potential indicators of screening performance.

Methods: The proportional incidence of T2+ cancers (observed/expected cases) in a population-based screening programme (Trento, 2001-2009) was estimated. A parallel review of 'negative' preceding mammograms for screen-detected T2+ and for all ICs, using 'blinded' independent readings and case-mixes (54 T2+, 50 ICs, 170 controls) was also performed.

Results: T2+ cancers were observed in 168 screening participants: 48 at first screen, 67 at repeat screening and 53 ICs. The T2+ estimated proportional incidence was 68% (observed/expected = 168/247), corresponding to an estimated 32% reduction in the rate of T2+ cancers in screening participants relative to that expected without screening. Majority review classified 27.8% (15/54) of T2+ and 28% (14/50) of ICs as screening error (P = 0.84), with variable recall rates amongst radiologists (8.8-15.2%).

Conclusions: T2+ review could be integrated as part of quality monitoring and potentially prove more feasible than IC review for some screening services.

Key Points: • Interval breast cancers, assumed as screening failures, are monitored to estimate screening performance • Large (T2+) cancers at screening may also represent failed prior screening detection • Analysis of T2+ lesions may be more feasible than assessing interval cancers • Analysis of T2+ cancers is a potential further measure of screening performance.