Abstract 3268: Proteomic response in breast cancer treated with neoadjuvant chemotherapy with and without bevacizumab: Reverse phase protein array (RPPA) results from NeoAva - a randomized phase II study

BACKGROUND: In this phase II clinical trial, patients with HER2 negative primary tumors of ≥25 mm were treated with neoadjuvant chemotherapy (4 x FEC100 + 12 weeks of taxane-based therapy) and randomized (1:1) to receive bevacizumab or no bevacizumab. Mammography, ultrasound and MR imaging were used for response evaluation, in addition to final pathology assessment. HYPOTHESIS: RPPA proteomic analyses support identification of molecular mechanisms associated with clinical response to bevacizumab treatment. METHODS: Tumor responses were evaluable in 132 patients; of which 66 received bevacizumab. Ratio of the tumor size at final pathology assessment, and at inclusion was calculated to obtain a continuous scale of response reflecting the percentage of tumor shrinkage in response to therapy. Tumor material was obtained at screening, 12 weeks into treatment and at surgical removal of tumors at 25 weeks. Lysates from each sample was analyzed on reverse phase protein arrays (RPPA) for expression levels of 210 proteins of which 54 were phospho-specific. Data from protein analyses was compared to previously generated mRNA expression data. RESULTS: Several proteins were found for which expression prior to treatment (week 0) reflected a better response on tumor shrinkage in the combination treatment arm (chemotherapy+bevacizumab): E.g. good responders had lower PDGFR-beta expression, and this was also observed at the mRNA level, while this result was not identified in the mono treatment arm (chemotherapy alone) on either level. The proteomic response from week 0 to 12 in both treatment arms had an overall similar profile regarding up- and down-regulated proteins; however, the combination treatment (FEC100 + bevacizumab) induced substantially more effect on regulation of each protein. This might reflect the capability of bevacizumab treatment to potentiate the effects of the anthracyclin based chemotherapy from week 0 to 12. Conversely, from week 12-25 (taxane-based therapy + bevacizumab) this effect was lost or even reversed, and reveals a possible need for further studies investigating changes in protein expression and correlation to response of a given treatment. Of particular interest were proteins that switched direction of regulation between the FEC and taxane-based regimes, however, these effects were not confined to the combination treatment and thus probably not due to the added bevacizumab. We are in the process of analyzing the impact of phosphorylation and thus protein activation states on treatment response. The above mentioned results have potentially important clinical relevance and will be further investigated with respect to subtypes and the biological pathways affected by antiangiogenic therapy. Citation Format: Mads H. Haugen, Ole Christian Lingjaerde, Marit Krohn, Evita M. Lindholm, Laxmi Silwal-Pandit, Elin Borgen, Oystein Garred, Anne Fangberget, Marit M. Holmen, Ellen Schlichting, Helle Skjerven, Steinar Lundgren, Erik Wist, Bjoern Naume, Gunhild M. Maelandsmo, Yiling Lu, Anne-Lise Boerresen-Dale, Gordon B. Mills, Olav Engebraaten. Proteomic response in breast cancer treated with neoadjuvant chemotherapy with and without bevacizumab: Reverse phase protein array (RPPA) results from NeoAva - a randomized phase II study. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3268.