Interval and non-compliant breast cancers diagnosed in women aged 50–69 in a Canadian breast cancer screening program: Clinical-pathologic correlations

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21060 Background: Assessment of interval breast cancers and screening compliance are important parameters in the assessment of any comprehensive breast screening program. Clinical-pathologic examination of interval cancers may also be helpful in understanding differences between screen-detected and interval disease. The Nova Scotia Breast Screening Program (NSBSP) was founded in 1991 and, as of Jan 2007, 86,071 women aged 50–69 have entered the program, with 255,350 screening examinations completed. Methods: The Mammography Information System and Diagnostic Reporting System databases were used to identify all interval (diagnosed after a negative screen and before the recommended next screen) and non-compliant (diagnosed after a negative screen and after the recommended next screen) invasive breast cancer diagnoses. Unpaired t-tests were used to compare age at diagnosis, detection time and tumor size and the Chi- square test was used to compare the odds ratio of nodal involvement between interval and non-compliant cases. Results: A total of 1,189 screen-detected, 309 interval and 260 non-compliant invasive breast cancers were diagnosed amongst program participants aged 50–69 over this time period. Mean values (standard deviation, SD) for interval vs. non-compliant cases were; age at diagnosis 58.8 (SD=5.6) vs. 59.6 (SD=5.9) years (p=0.113); time to detection from last screen 363.9 (SD=187.6) vs. 1296 (SD=868.4) days (p<0.0001); tumor size 15.9 (SD=15.0) vs. 14.6 (SD=14.7) mms. (p=0.342). The incidence of nodal involvement in interval vs. non-compliant breast cancers was 32% and 23.5% respectively resulting in an odds ratio of 1.54, p=0.023. Conclusions: Interval and non-compliant breast cancers made up a significant proportion of all invasive cancers diagnosed amongst program participants. The finding of more cases having involved nodes at diagnosis despite no significant difference in mean age at diagnosis or tumor size suggests that interval disease may have a more aggressive phenotype. Data on tumor grade, lymphovascular invasion, hormone receptor status and HER2/neu over-expression are being collected. No significant financial relationships to disclose.