BACKGROUND: Many studies have investigated the survival of women by comparing those who participated in organised screening with those who did not. However, among those who do not participate in organised screening, some women undergo opportunistic screening, but these women remain difficult to identify, particularly in France. Therefore, the aim of this study was to identify opportunistic screening, and then to study survival after breast cancer separately according to participation in organised, opportunistic or no screening, and taking into account sociodemographic inequalities. METHODS: The study population was identified from 3 French cancer registries, whose data was crossed with the screening coordination centers and the National Health Data System to identify the different type of screening. The European Deprivation Index was used to define the level of deprivation. We estimated net survival using the Pohar-Perme method. RESULTS: The 5-year net survival probabilities were higher for women who attended organised screening (97.0 %) than for women with opportunistic screening (94.1 %) or non-attenders (78.1 %). According to the level of deprivation, a significant difference was observed between the groups of women screened by organised and opportunistic screening, compared to the non-attenders. CONCLUSION: The identification of opportunistic screening is an important element in identifying women who do not screening. It enables to us to see that women who do not attend any screening have a much higher loss-of-opportunity in terms of survival than those who participate in organised or opportunistic screening, and even more so in the most deprived areas.Read less <