First mammography screening participation and breast cancer incidence and mortality

This population-based cohort study evaluated the long-term relationship between initial participation in mammography screening and subsequent breast cancer outcomes among approximately 432,000 women in Stockholm, Sweden. Women were invited to their first screening between 1991 and 2020 at ages 40 or 50 and followed for up to 25 years through national health registries. Overall, 32% did not attend their initial screening. Non-attenders were significantly less likely to participate in later screening rounds and were more likely to be diagnosed with advanced disease, showing 1.5-fold higher odds of stage III and more than 3.5-fold higher odds of stage IV breast cancer compared with attenders. Although cumulative 25-year breast cancer incidence was similar between groups (7.6–7.8%), breast cancer–specific mortality was markedly higher among non-attenders (adjusted HR 1.40; 95% CI 1.26–1.55). These findings indicate that missing the first mammography screening is associated with delayed detection and worse survival, underscoring the importance of promoting early participation as a key strategy in population-based breast cancer.