ERalpha-status of disseminated tumour cells in bone marrow of primary breast cancer patients

Introduction Isolated disseminated tumour cells (DTC) are regarded as surrogate markers for minimal residual disease in breast cancer. Characterisation of these cells could help understand the known limitations of adjuvant therapy. Of particular interest is their oestrogen-receptor (ER) status because endocrine adjuvant therapy remains a cornerstone of breast cancer treatment. Methods Bone marrow (BM) aspirates from 254 patients with primary breast cancer were included in this study. A double immunofluorescence staining procedure was established for the identification of cytokeratin (CK) positive/Er alpha-positive cells. ER alpha status of the primary tumour was assessed immunohistochemically using the same antibody against ERa. Results In 107 of 254 (42%) breast cancer patients, CK-positive cells could be detected in the BM. More than one DTC in the BM was observed in 38 of the 107 patients. The number of detected cells ranged between 1 and 55 cells per 2 x 10(6) mononuclear cells. DTCs demonstrated ER alpha positivity in 12% of the patients. The ER alpha expression was heterogeneous in 10 of the 38 (26%) patients with more than one DTC. The concordance rate of ER alpha status between primary tumour and DTC was 28%. Only 12 of 88 patients with ER alpha-positive tumours also had ER alpha-positive DTCs. Conclusions Primary tumours and DTCs displayed a concordant ER alpha status in only 28% of cases. Most of the DTCs were ER alpha negative despite the presence of an ER alpha-positive primary tumour. These findings further underline the distinct nature of DTCs and may explain the failure rates seen in conventional endocrine adjuvant therapy.