Clinical outcomes by breast cancers diagnostic modes: A comprehensive evaluation of a national breast cancer screening programme

Introduction: Breast cancer is the leading cause of diagnosis and cancer-related death among women in almost every country worldwide. To reduce and to control breast cancer mortality, Luxembourg implemented the Programme Mammographie, a population-based organised programme in 1992. We aimed to compare the clinical and screening characteristics of breast cancers diagnosed in Luxembourg's eligible screening population by detection modes. Methods: 1618 women aged 50–71 diagnosed with a first breast cancer between 2013 and 2018 were included from Luxembourg National Cancer Registry (Registre National du Cancer, RNC). The detection mode (screen-detected, interval-detected, and diagnosis-detected) is determined by linking RNC data with 144,270 participations in the Programme Mammographie between 2011 and 2018. Results: Screen-detected breast cancers were diagnosed at younger ages, more often found in situ, at a lower stage at diagnosis, smaller, showed less lymph node invasion, and were more frequently treated with conservative surgery than diagnosis-detected. Interval-detected cases had the lowest proportion of in situ cancers and displayed distinct molecular subtypes usually considered as more aggressive. Cancers found after the initial round of participation had worse prognosis than those found after subsequent rounds. Interval cancers diagnosed during the second year had worse prognosis than those diagnosed in the first year after participation. The best prognosis was identified in screen-detected cases whose participation was on time regarding the penultimate, and the worst in diagnosis-detected with no participation over the period. Conclusions: Regular participation in the Programme Mammographie is associated with earlier detection and less advanced forms of breast cancer at diagnosis. However, healthier behaviors among screening participants might also contribute to these outcomes. The indicators produced supports public health policies to further increase its level of effectiveness.