10557 Background: Selection of patients for treatment with trastuzumab is currently based on the semi-quantitative measurement of HER2 protein expression (IHC) or gene amplification (FISH). We made quantitative measurements of HER2 expression and homodimerization using a novel assay, eTag, and correlated them with overall survival (OS) and time-to-progression (TTP) following trastuzumab treatment in a cohort of patients with metastatic breast cancer (MBC). We also examined the benefit of concomitant chemotherapy (CT) depending on quantitative HER2 expression. Methods: The Jules Bordet cohort (Brussels, Belgium, N=71) had MBC and prior treatment with at least two CT regimens. Patients received trastuzumab alone or combined with predominantly paclitaxel. Independent medical data review and central confirmation of HER2 overexpression by FISH (N=64) or IHC (N=7) were mandatory. The eTag assay was used to quantitate HER2 protein expression and HER2:HER2 dimers in FFPE specimens. eTag measurements were correlated with OS and TTP using Kaplan-Meier and Cox Proportional Hazards regression analyses. Results: Cox analyses identified three independent correlates of OS and TTP: number of metastatic sites (HROS = 2.4/site, 95%CI 1.5–3.9, p = 0.00019), treatment with trastuzumab only (HROS = 2.8, 95%CI 1.1–7.3, p = 0.036), and HER2 expression level (HROS = 0.24/log10(HER2), 95%CI 0.09–0.7, p = 0.0058). Patients with high HER2 (above median expression) experienced better OS than those with low HER2 (HR 0.24, p = 0.0014). Patients with high HER2 expression did not benefit from added CT (HR = 0.95, 95%CI 0.24–3.8, p = 0.94), while patients with low HER2 expression did (trastuzumab alone HR 4.4, 95% CI 1.3–18, p = 0.018). Similar results were observed for HER2:HER2 dimerization. Conclusions: Within a population of patients selected by FISH or IHC to receive trastuzumab, higher HER2 expression or HER2:HER2 dimerization correlated with better outcomes. Patients with high HER2 expression derived no benefit from concomitant CT, while patients with low HER2 expression benefited significantly from the addition of CT to trastuzumab. No significant financial relationships to disclose.
A guided and personalised treatment in metastatic breast cancer: Optimisation of gene and protein expression in tumor tissue
