Comparison of HER2 extra cellular domain (ECD) serum level at the time of metastasis with HER2 status modification between primary breast cancers and their respective metastases

Abstract

1030 Background: Modification of HER2 level of expression/amplification between primary breast cancer and late metastasis was reported as a rare event. We investigated the usefulness of HER2 ECD serum level assessment at the time of metastasis to identify modification of HER2 status in the metastatic tissue. Methods: We performed a retrospective comparison of HER2 level of expression/amplification on paraffin-embedded tissues from 69 patients of both primary breast cancers and their distant metastasis using immunohistochemistry (IHC) (CB11, Ventana) and chromogenic in situ hybridization (CISH) (Zymed). For 60 patients, frozen serum at time of metastasis was available and HER 2 ECD serum level was measured with an Elisa commercial kit (Oncogene Science); we used 15ng/ml as cut-off value. Results: Among the 69 primary tumors, 9 were HER2 positive, 7 on IHC and 7 on CISH (but 2 of these were only 2+ on IHC). There were 13 metastatic HER2 positive lesions (7 on IHC, 9 on CISH and 3 positive using both methods...