Estrogen receptor (ER) status of disseminated tumor cells in the bone marrow of breast cancer patients

Abstract

21013 Background: The presence of disseminated tumor cells (DTC) in bone marrow (BM) of primary breast cancer patients is associated with poor prognosis. These patients may benefit from adjuvant endocrine therapy since cytotoxic agents are not able to completely eliminate DTCs as previously shown. Only patients with hormone receptor positive breast cancer are eligible for hormonal treatment. The ERa status is routinely defined in primary tumor tissue. However, the ERa status of DTC may differ compared to the primary tumor. Therefore, the aims of this study were (1) to determine the ERa status of DTC in BM of breast cancer patients, (2) and to compare the ERa status of DTC and corresponding primary tumors. Methods: BM aspirates from 251 primary breast cancer patients were included into the study. A double immunofluorescence staining procedure was established for the identification of cytokeratin-positive (CK)/ERa positive cells. ERa status of the primary tumor was immunohistochemically assessed using the same antibody against ERa. Results: In 105 of 251 (42%) breast cancer patients CK-positive cells could be detected in BM. The number of detected cells ranged between 1 and 13 / cells per 2*106 mononuclear cells. Disseminated tumor cells demonstrated ERa positivity in 13 (12%) of these 105 patients. The ERa expression on DTC was heterogeneous in 10 of 13 (79%) patients. Concordance rate of ERa status between primary tumor and DTC was 27%. Only 11 of 83 patients with ER a positive tumors had also ERa positives DTC. Conclusions: (1)The hormone receptor status between primary tumor and corresponding DTC is disconcordant. (2)This discrepancy may explain the rate of non-responders to adjuvant endocrine therapy despite ER-positive primary tumors. (3)These patients may benefit from adjuvant therapy regimens based on antibody strategies or bisphosphonates. No significant financial relationships to disclose.