Comparison of HER2 status between disseminated tumor cells (DTC) and corresponding tumors in breast cancer patients

Abstract

Aims: Breast cancer patients with tumor cell persistence in the bone marrow may benefit from a secondary adjuvant immunotherapy. HER2 protein is suggested as one of those promising targets. However, the antigen pattern of disseminated cells (DTC), to which immunotherapy might be targeted, could differ from the antigen profile of the primary tumor. Therefore, the aims of this study were (a) to determine the HER2 status of DTC and (b) to compare the HER2 status between DTC and corresponding primary tumors. Methods: 135 primary breast cancer patients were included in this study. The isolation of DTC was performed by density centrifugation through Bicoll. To assess the HER2 status of DTC, an immunofluorescent double staining procedure was performed. The DTC were detected by the pan anti-cytokeratin antibody C11 conjugated to FITC and double labeled with polyclonal rabbit antibody CB 11 against the HER2 antigen. CB11 was detected by a secondary antibody conjugated to Texas Red. The HER2 status of the primary tumor was assessed by the HERCEP-test (Dako Co., CA). Results: 58 of 135 patients had DTC in the bone marrow. In 24 of these patients, HER2 positive DTC could be detected. The HER2 expression was heterogeneous in 11 of 23 patients with two or more tumor cells. HER2 positivity (score +2/+3) could be demonstrated in 12 of 55 primary tumors. The concordance rate between primary tumor and DTC was only 67%. HER2 positive DTC were detected in 15 patients with HER2 negative (0/+1) tumors. In contrast, three patients with HER2 positive primary tumors had HER2 negative DTC. Conclusion: (1) The HER2 status of DTC and corresponding primary tumor can differ. Therefore, the decision for antibody based strategies should also be based on the HER2 status of DTC. (2) The HER2 expression of DTC is heterogeneous in individual patients which may reduce efficacy of an immunotherapy based strategy only directed against HER2.