Background: Studies of Her-2/neu protein expression in interval and screen-detected breast cancers have been conflicting. Therefore we assessed the Her-2/neu amplification status in these groups by using in situ hybridization.
Patients and methods: The Her-2/neu oncogene amplification and protein over-expression were compared in 79 screen-detected and 39 interval breast carcinomas, using a novel and well-documented chromogenic in situ hybridization (CISH) method and immuhistochemistry.
Results: There were 33% CISH-positive cases in the interval cancer group and only 4% CISH-positive cases in the screen-detected group. The odds ratio for interval cancer was 14.1 (95% CI 2.2 to 91.0) in the CISH-positive tumours compared with CISH-negative tumours after adjustment for nodal status, tumour size and histological grade.
Conclusion: Our results indicate, for the first time, that there is a clear-cut difference in Her-2/neu amplification between screen-detected and interval breast carcinomas. The amplification appears to be a rare event in screen-detected cancers but distinctly frequent in interval cancers when compared to cancers described in earlier studies.