HER2 gene status assessment in micrometastatic cells in bone marrow (BM) of breast cancer patients by fluorescence in situ hybridization (FISH)

Abstract

9520 Background: Detection of micrometastatic cells in BM of breast cancer patients has been shown to be an independent prognostic factor. HER2 overexpression occurs in 15% to 30% of breast cancers. HER2 overexpression on micrometastatic cells has been reported in 60% of the patients, independently of primary tumor status (Braun, S. Cancer Res., 61, 2001, 1890). In metastatic breast cancer patients, a rate of 100% of HER2 positive micrometastatic cells has been reported (Pantel, K., JNCI, 85, 1993, 1419). These results were obtained by immunocytochemical double labeling techniques with anti-cytokeratin and HER2 antibodies. The aim of this study was to assess HER2 status in micrometastatic cells in BM of breast cancer patients by FISH and to compare it to primary tumor status. Methods: Disseminated micrometastatic cells were detected in BM aspirations from breast cancer patients in a prospective series. The pancytokeratin (CK) monoclonal antibody A45-B/B3 was used and CK+ cells were detected by an automated cellular imaging system (ACIS) (ChromaVision Medical System). Positive samples of BM for micrometastatic cells (CK+) detection and their corresponding primary tumors, were obtained from 27 patients (3 stage II, 1 stage III and 23 stage IV). HER2 status of micrometastatic cells in BM was assessed by FISH. HER2 status of primary tumor was assessed by immunohistochemistry (CB11 antibody) and confirmed by FISH in ++ cases. Results: 5/27 (18.5%) patients had HER2 overexpression in primary tumors and 4/27 (15%) (CI 95%: 2–28%) had HER2 amplification in micrometastatic cells in BM. Concordance rate between primary tumor and bone marrow status was 90%. In 2 cases HER2 was overexpressed in primary and not in distant BM cells and in one case, HER2 was amplified in BM tumoral cells (6 copies) and not in primary. In four additional cases, chromosome 17 trisomy was detected in BM micrometastatic cells without amplification of HER2. Conclusions: The HER2 status assessed by FISH in metastatic isolated BM cancer cells is highly correlated with primary tumor status. Our study confirmed the stable status of HER2 during the metastatic process. No significant financial relationships to disclose.