Journal of Clinical Oncology, 2008 ASCO Annual Meeting Proceedings (Post-Meeting Edition).
Vol 26, No 15S (May 20 Supplement), 2008: 638
© 2008 American Society of Clinical Oncology

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Abstract

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

Queen Elizabeth II Health Sciences Centre, Halifax, NS, Canada; Dalhousie University, Halifax, NS, Canada; Capital District Health Authority, Halifax, NS, Canada

638

Background: The interpretation of clinical and biologic differences between screen-detected and interval breast cancers has been limited by the failure to control for factors known to influence breast cancer biology, such as age at diagnosis, as well as for differences in recommended screening intervals between age groups. Methods: A case-control study nested within the participants of the population-based Nova Scotia Breast Screening Program diagnosed between ages 40–69 in the period 1991–2006 was performed. Interval cases were selected as having developed after a negative screen and prior to the recommended next screen and were validated by blinded review of the pre-diagnosis screening mammogram by 3 mammographers, 2 of whom had to agree that the screening exam was negative. Screen-detected cases were matched to intervals on a 2:1 basis by 5-year age group and recommended screening interval (40–49 yo, annual; 50–69 yo + family history, annual; 50–69 yo - family history biennial). Results: 240 interval cancers were identified of which 38% were grade 3 lesions and 31.7% had LVI. Selected comparisons to controls are presented in Table 1. For those with currently available data, ER/PR/HER2 results (intervals vs screen-detected) were; ER+ 73% vs 78.5%, PR+ 65.4% vs 72.5%, HER2+ 17% vs 26.7%. Conclusions: Controlling for age and screening interval, interval breast cancers are significantly larger and significantly more frequently node-positive at diagnosis compared to screen-detected cancers. They are also more likely to be of lobular histology and have a triple-negative phenotype.

No significant financial relationships to disclose.

Abstract presentation from the 2008 ASCO Annual Meeting