Abstract P1-08-27: Quantitative analysis of tumor expression of phosphoproteins from PI3-kinase and MAP-kinase signaling pathways as biomarkers of the biological and clinical activity of trastuzumab and everolimus in breast cancer: Unicancer RADHER phase II trial results

Abstract Background: PI3-kinase (PI3K) and MAP kinase (MAPK) are the main signaling pathways implicated in molecular oncogenesis. In breast cancer, inhibition of these signaling pathways has been largely envisaged by means of targeted therapy. Unicancer RADHER study aimed at evaluating the efficacy of adding everolimus (E) to trastuzumab (T) as preoperative therapy for primary HER2+ operable breast cancer patients and to evaluate molecular response biomarkers. We report here the investigation of the expression of phosphoproteins from PI3K and MAPK signaling pathways as predictive biomarkers of clinical and pathological response as well as pharmacodynamic markers of treatment activity. Methods: 82 eligible patients were randomized to receive T alone (loading dose 4 mg/kg, then 2 mg/kg/week), or T+E (10 mg/day) for a 6-week pre-operative treatment. Clinical response rate (cRR) was determined from OMS criteria with complete and partial responses being considered as “ responders “ and stable and progressive diseases as “ non responders “. Pathological response rate was evaluated according to Sataloff classification, with Ta and Tb being considered as “ responders “ and, Tc and Td as “ non responders “. The expression levels of phosphorylated-AKT (p-AKT), p-GSK3b, p-S6 kinase, p-MEK1, p-ERK1/2, p-P90RSK, p-IGF1R as well as p-P38MAPK were quantitatively assessed using multiplex bead immuno-assay. All patients had baseline needle frozen biopsies taken before initiation of the treatment, at cycle 4 as an option and at surgery. Before being submitted to total protein extraction, all biopsies were validated by a senior pathologist after HE slide examination to ensure a tumor content >50%. 36 pairs associating baseline + surgery tumor specimens and 4 pairs of baseline + cycle 4 biopsies were eligible for protein extraction. Results: No statistically significant relationship was observed between the expression level of any of the phosphoproteins in the initial biopsies and neither the clinical nor the pathological response, overall. After treatment, as compared to the level of expression measured in the initial biopsies, a significant increase of p-GSK3β, p-MEK1, p-ERK1/2, p-P38MAPK was observed in T+E arm and a significant decrease in p-S6 kinase expression in the global patient population. No significant variation was observed in T arm. Additional analysis with immunohistochemistry data is planned and will be presented. Conclusion: In the present study, measuring phosphoproteins expression showed that combining E with T, altered the regulation of signaling proteins from PI3-Kinase and MAP-kinase pathways. No response predictive biomarker could be identified among the phosphoproteins analyzed tending to show that the clinical and pathological response to T and T+E should be driven by additional mechanisms. As a whole, these results validate the use of multiplex bead immuno-analysis for determination of phosphorylated signaling proteins in clinical needle biopsies from breast cancer specimens and its prospective evaluation as biomarker for the activity of targeted therapies. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P1-08-27.