gms | German Medical Science

Background: The presence of disseminated tumor cells (DTC) in the bone marrow (BM) of breast cancer patients is associated with a less favorable prognosis. Studies have indicated that these patients could potentially benefit from secondary adjuvant immunotherapy. HER2 protein is considered a promising target. The HER2-phenotype of the primary tumor is currently the diagnostic gold standard to determine eligibility for antibody based treatment decisions. However, existing data indicate that the antigenic profile of primary tumors and DTC might be different. The aim of this study was, first to determine HER2 overexpresson on DTC in the BM of breast cancer patients and second to compare HER2 status of disseminated tumor cells and corresponding primary tumors.

Material and Methods: Cytospins from 124 primary breast cancer patients (stage I-III) were included in the study. A double labeling procedure was used for the identification of cytokeratin-(CK)-positive/HER2 positive cells. Slides were incubated with the pan-anti-cytokeratin antibody C11 conjugated to FITC and the polyclonal rabbit antibody CB11 against the HER2 protein. CB11 was detected by a secondary antibody labeled with TexasRed. Slides were analyzed manually by fluorescence microscopy. HER2 status of the primary tumor was immunohistochemically assessed by the HERCEP-test (Dako Co. Carpinteria Ca).

Results: CK-positive cells were detected in the bone marrow of 47 patients. The number of DTC ranged from 1 to 70 per slide. With regard to the primary tumor HER2 positivity (2+/3+) was demonstrated in 12 of 47 primary tumors. 24 of 47 (51%) patients had HER2 positive DTC. Concordance rate between primary tumor and disseminated tumor cells was 63%. In three patients with HER2 positive tumors HER2 negative tumor cells were detected. In contrast, 14 patients with HER2 negative tumors (0/1+) had HER2 positive cells. The HER2 expression on disseminated tumor cells was heterogeneous in 8 of 20 patients with more than one cytokeratin-positive cell.

Conclusion: (I) HER2 positive DTC can be detected in patients with HER2 negative primary tumors. Therefore, the antigenic profil of disseminated tumor cells could become a co-determinant of treatment decision for adjuvant or secondary adjuvant antibody based strategies. (2) The HER2 overexpression on disseminated tumor cells is heterogenous in individual patients which may reduce the efficay of an immunotherapy based strategy directed against only the HER2-antigen. The identification of additonal targeting molecules will be necessary to control residual disease.