Clinical-pathologic characteristics and outcomes of true interval compared to screen-detected breast cancer among participants in a Canadian breast screening program: A nested case-control study

6528 Background: It has been hypothesized that, compared to screen-detected breast cancer (Scr), true interval breast cancers (Int) are associated with adverse prognostic factors and outcomes. Data has remained controversial due to failure to control for age at diagnosis and screening interval as well as lack of information regarding adjuvant therapies and inclusion of other categories of interval cancers (e.g., missed or noncompliant). Methods: A case-control study nested among participants of the population-based Nova Scotia Breast Screening Program diagnosed with invasive disease between the ages 40–69 in the period 1991–2006 was performed. Ints were validated by blinded review of the pre-diagnostic screening mammogram by 3 mammographers, 2 or 3 of whom had to agree that it was negative for inclusion as a true Int. Scrs were matched to Ints on a 2:1 basis by 5 year age group at diagnosis and screening interval (40–49 yo, annual; 50–69 yo + family history, annual; 50–69 yo - family history, biennial). R...