Background: Multi-drug resistance to chemotherapeutic agents, as well as resistance to radiation therapy is a major cause of treatment failure in breast cancer. The expression of the excision repair cross-complementation 1 (ERCC1) enzyme in tumor tissue has been associated with resistance to platinum based chemotherapy but also with radiation therapy in different cancer diseases. However, studies on ERCC1 in breast cancer are limited. Furthermore, after primary tumor resection, there is no validated clinical parameter to predict the sensitivity to radio/chemotherapy. Circulating Tumor Cells (CTCs), as potential surrogate markers for minimal residual disease, would be an ideal ‘surrogate tissue’ to identify such biomarkers. Here we evaluated ERCC1 expression in CTCs of primary and metastatic breast cancer patients as a potential biomarker for radio/chemoresistance and correlated these findings with the presence of HER2-positive and stemness like CTCs (slCTCs), including cells being able to perform epithelial-mesenchymal transition (EMT).

Patients and Methods: 2 × 5 ml blood from primary (n = 110) and metastatic (n = 56) breast cancer patients were analyzed for CTCs with the AdnaTest BreastCancer (AdnaGen AG, Hannover, Germany) for the detection of EpCAM, MUC-1, HER-2, and beta-Actin transcripts. The recovered c-DNA was additionally tested for the presence of a) ERCC1 b) slCTCs using the AdnaTest TumorStemCell for the expression of ALDH1 (both using single-plex RT-PCR) and c) CTCs in EMT applying the AdnaTest EMT (multiplex RT-PCR for TWIST, AKT2, PI3K). The analysis of PCR products was performed by capillary electrophoresis on the Agilent Bioanalyzer 2100.

Results: In primary breast cancer, the overall detection rate for CTCs was 27% (30/110 patients) with the expression rate of 83% for HER2. ERCC1 was detected in 51/110 patients (46%), slCTCs in 27/110 patients (25%) and CTCs in EMT in 47/110 patients (43%), respectively. ERCC1 expression was significantly associated with the presence of HER2-positive CTCs (p = 0.001), slCTCs (p = 0.014) and CTCs in EMT (p = 4×10E-8), respectively. In metastatic breast cancer, the positivity rate for CTCs was 36% (20/56 patients) with the expression rate of 40% for HER2. ERCC1 was detected in 15/56 patients (27%), slCTCs in 16/56 patients (29%) and CTCs in EMT in 12/56 patients (22%), respectively. ERCC1 expression was significantly associated with the presence of HER2-positive CTCs (p = 0.0019), slCTCs (p = 0.00014) and CTCs in EMT (p = 0.00037), respectively.

Conclusion: The tumor stem cell phenotype and EMT are widely discussed to be correlated with increasing cell survival and chemotherapy resistance including increased DNA repair capacity characterized by the overexpression of genes like ERCC1. Using CTCs as a potential surrogate marker for radio/chemoresistance, we could show a significant correlation of the ERCC1 profile and CTCs displaying tumor stem cell or EMT characteristics but also a HER2-positive phenotype. Thus, the presence as well as the molecular profile of CTCs might become an important tool to predict radio/chemoresistance in breast cancer patients. The clinical relevance on prognosis and therapy response has to be evaluated in a prospective trial.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P1-04-13.