Abstract OT1-12-04: A phase IIIb, open-label, local, multicenter study of the molecular features of postmenopausal women with hormone receptor-positive (HR+) HER2-negative advanced breast cancer on first-line treatment with ribociclib and letrozole (BioItaLEE)

Abstract

Background: characterizing the molecular features associated with prolonged benefit from CDK 4/6 inhibitors in HR+ HER2- BC and the acquired genomic alterations following treatment progression remains an unmet need and is crucial for leveraging the efficacy of CDK4/6 inhibitors and for elucidating resistance mechanisms. Identifying pre-treatment or pharmacodynamic predictive markers of treatment benefit, as well as predictive markers of toxicity by correlating pharmacogenomics with adverse events, could help physicians to select patients who may benefit the most from these therapies and improve the clinical management. Trial design: this is an Italian, multicenter, open-label, single-arm trial (NCT03439046) enrolling approximately 350 HR+ HER2- aBC first line patients in 48 sites. Patients are treated with ribociclib and letrozole and eligibility criteria are similar to the MONALEESA-2 trial. Patients will be followed for safety and efficacy outcomes. An extensive prospective collection of biological samples at different time points will be performed as follow: whole blood and plasma at baseline, cycle 1-D15, cycle 2-D1, at first imaging evaluation, at cycle 24-D1, as well as upon progression of disease; newly obtained tissue biopsies at baseline and at progression; a buccal swab for pharmacogenetics at baseline. Efficacy and safety data will be collected for all patients. Aims: the primary objective of this study is to identify circulating tumor DNA (ctDNA) alterations at baseline, to describe their evolution during treatment and to evaluate the association with clinical outcome. An optimized Next Generation Sequencing approach for the detection of low abundance events in ctDNA will be adopted. Single nucleotide variants and copy number alterations in a customized panel of genes relevant for BC will be analyzed. Secondary objectives include the evaluation of: serum thymidine kinase 1 activity over time as blood marker of early response; ctDNA alterations across different patient profiles and clonal evolution of ctDNA alterations under treatment; ctDNA alterations at time of tumor progression; correlation between mutational status detected in ctDNA and matched tissue samples; features of tumor microenvironment before and after treatment; association of pharmacogenomics patterns with adverse events and clinical outcomes. Clinical efficacy and safety of ribociclib + letrozole will be correlated with all biological endpoints. Statistical methods: the study is descriptive in nature and no formal statistical testing is necessary or applicable. Sample size is aligned with other biomarker studies and is based on a feasibility analysis of the trial and relative timelines. Present accrual: The first study patient was screened in Feb 2018, as in June 2018, 126 patients have been screened and 78 patients have been enrolled. Citation Format: De Laurentiis M, Arpino G, Bianchini G, Malorni L, Castelletti D, De Vecchi R, Grasso D. A phase IIIb, open-label, local, multicenter study of the molecular features of postmenopausal women with hormone receptor-positive (HR+) HER2-negative advanced breast cancer on first-line treatment with ribociclib and letrozole (BioItaLEE) [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr OT1-12-04.