Abstract OT1-1-02: PI3K-Akt-mTOR pathway analysis to obtain further insight in the efficacy of everolimus in combination with exemestane in metastatic, ER-positive breast cancer: A Dutch breast cancer research group (BOOG) study

Abstract

Abstract Background In patients with hormone receptor-positive breast cancer, activation of the PI3K-Akt-mTOR pathway is associated with resistance against endocrine therapy. Previous research has shown that genetic aberrations in this pathway occur frequently, including mutation and/or amplification in PI3K subunits or PI3K effectors as well as loss of lipid phosphatases (Fu X, et al. The Breast; 2013). Central review of the BOLERO-2 randomized phase III trial in which patients refractory to a non-steroidal aromatase inhibitor were randomized between exemestane combined with the mTOR inhibitor everolimus versus exemestane and placebo has shown a progression-free survival (PFS) of, respectively, 11.0 and 4.1 months [hazard ratio = 0.38 (95% confidence interval 0.31-0.48; log-rank P <0.0001)] (Yardley DA, et al. Adv Ther; 2013). The combination, however, is known to cause more adverse events and is associated with additional costs as compared to exemestane alone. In the present study we will explore whether there are biomarkers that might indicate which patients most likely benefit from co-targeting PI3K and ER pathways. Trial design/Aims This is a Dutch prospective, open-label, single-arm, investigator-initiated, multicenter trial in which approximately 30 hospitals will participate. A total of 175 patients will be included for baseline blood sampling and archival tumor tissue collection. From 50 patients, a fresh tumor biopsy is required at baseline and from 30 out of 50, another tumor biopsy will be collected upon progressive disease. Exploratory biomarker assessment includes immunohistochemistry (total and phosphorylated PI3K, AKT, mTOR, p70S6K and 4EBP1), tissue phosphoproteomics and circulating tumor DNA (mutations). The results of the biomarker analysis will be compared with clinicopathological characteristics and PFS. Eligibility Postmenopausal patients with hormone receptor-positive, HER2-negative, locally advanced or metastatic breast cancer, refractory to anastrozole or letrozole will be included. No previous treatment with exemestane or mTOR inhibitor for advanced disease is allowed and Informed consent must be signed before enrollment. Statistical methods Since the majority of the tests involve the use of new techniques, the study will be mainly explorative in design. The association between potential biomarkers and clinicopathological characteristics will be tested using Fisher exact test or the Mann-Whitney test. PFS curves will be drawn using the Kaplan-Meier method. PFS in association with potential biomarkers will be tested using Cox proportional hazard regression analysis. Present and target accrual Recently, the study has been opened for inclusion. A period of 2 years is planned for patient enrollment. Up to May 2014, two patients were included. ClinicalTrials.gov identifier NCT02109913 Financial support is received from Novartis, the Netherlands. Citation Format: Dinja T Kruger, Karin Beelen, Connie R Jimenez, Maurice PHM Jansen, Stefan Sleijfer, Sabine C Linn, Epie Boven. PI3K-Akt-mTOR pathway analysis to obtain further insight in the efficacy of everolimus in combination with exemestane in metastatic, ER-positive breast cancer: A Dutch breast cancer research group (BOOG) study [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr OT1-1-02.