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Objectives: to evaluate the incidence of advanced-stage breast cancer (BC) - an early surrogate indicator of effectiveness of mammography screening - among women who attended the Friuli Venezia Giulia (FVG) Region (Northern Italy) screening programme compared to women who did not attend., Design: retrospective cohort study. Women invited to the first screening round (2006-2007) were identified from the database of the programme. The cohort was record-linked to the archive of women invited to the second round (2008-2009). The definition of attendance to screening was based on attendance to at least one of the two rounds. The incidence of BC was assessed through record linkage with the FVG cancer registry using an anonymous univocal identifier (end of follow-up: 31st December 2013). Three distinct definitions of advanced stage were used: pT2 or greater (pT2+), positive lymph nodes (pN+), and TNM stage II or greater (stage II+)., Setting and Participants: organized mammography screening programme for women aged 50-69 years in the five regional healthcare districts., Main Outcome Measures: incidence rate ratio (IRR) between attenders and non-attenders, adjusted for age and deprivation index, with 95% confidence interval (95%CI)., Results: the cohort included 104,488 attenders and 49,839 non-attenders. During follow-up (median duration 84 months), 2,717 invasive BCs were diagnosed among attenders and 1,149 among non-attenders. Total incidence rate was 13% higher among attenders (IRR 1.13; 95%CI 1.05-1.21). These, conversely, had a 36% lower rate of pT2+ BC (IRR 0.64; 95%CI 0.56-0.72), a 13% lower rate of pN+ BC (IRR 0.87; 95%CI 0.78-0.98), a 22% lower rate of stage II+ BC (IRR 0.78; 95%CI 0.70-0.87), and a 32% lower rate of mastectomy (IRR 0.68; 95%CI 0.60-0.78)., Conclusions: attenders had lower incidence rates of advanced-stage BC. This early effect is suggestive of a future impact of the screening programme on BC mortality.