A comparison of tumour characteristics of screen-detected and interval cancers and their relationship with breast density and AJCC prognostic stage in a UK screening cohort

OBJECTIVES: To compare tumour characteristics of screen-detected and interval cancers and their relationship with breast density and AJCC prognostic stage. MATERIALS AND METHODS: In this retrospective study, women screened with mammography between 1/4/2017 and 30/3/2020 at one site were included. Tumour characteristics were compared for screen-detected and interval cancers with breast density (Volpara) and AJCC (8th edition) prognostic stage for interval cancers. Categorical variables were compared using Pearson's χ², Fisher's exact, or binomial tests. RESULTS: From 55,010 attendees, 723 cancers were diagnosed (463 screen-detected; 260 interval). Time to interval cancer diagnosis was longer in women with dense breasts compared with non-dense breasts (median: 767 vs 624 days; p = 0.04). Earlier stage interval cancers ( < IIA) were more likely diagnosed in the second and third year compared to year 1 ((33/78) 48.7% and (56/129) 43.4% vs (12/53) 22.6%; p = 0.02). Retrospectively missed interval cancers were less frequent in women with dense breasts compared with true interval cancers (41.4% vs 71.9%); p < 0.01. Retrospectively missed intervals were more likely than true intervals to be grade 3 ((15/29) 51.7% vs (64/196) 32.7%, p = 1.00), lymph node positive ((12/29) 41.4% vs (70/196) 35.7%, p ≥ 0.7) and ≥ stage IIA ((14/29) 48.3% vs (72/196) 36.7%, ≥ IIA, p = 0.68). CONCLUSIONS: The time to interval cancer diagnosis was longer for women with dense breasts. Interval cancers presenting within the first year after screening had the worst prognosis. Retrospectively missed interval cancers had worse prognostic features and were more likely in non-dense breasts. KEY POINTS: Question To establish the relationship between screen-detected and interval cancers and breast density, and the prognosis of interval cancers depending on time of diagnosis and radiological signs. Findings Interval cancers presented later in women with dense breasts, but prognostically worse cancers presented earlier and were more likely to demonstrate retrospectively visible mammographic signs. Clinical relevance Our finding that prognostically worse interval cancers were most likely in the first year after screening, and when radiological signs were retrospectively present, identifies an important opportunity for AI-based tools to enhance screening programmes.