mRNA expression profiles in circulating tumor cells (CTCs) of patients with metastatic breast cancer (MBC) treated with aromatase inhibitors (AI).

11045 Background: Enumeration of CTCs can be used to assess prognosis in MBC and to evaluate treatment response. Besides enumeration, molecular CTC characterization is a promising tool to develop a more personalized treatment approach. Here, we evaluated the association between mRNA expression of currently known CTC-specific genes and response to first-line AI in MBC patients with estrogen receptor (ER)+ primary tumors. Methods: CTCs were isolated and enumerated from blood of 25 MBC patients before first-line therapy with an AI. Fourteen patients received a non-steroidal AI (8 letrozole, 6 anastrozole) and 11 patients were treated with exemestane. mRNA expression levels of 96 genes were measured by quantitative RT-PCR as previously described (Sieuwerts et al. Clin Cancer Res. 17:3600-3618, 2011). Expression levels of these genes were studied for their association with time to progression (TTP) after start first-line AI. Results: Median TTP was 338 (range 14–1,239) days. Median baseline CTC count for the 2...