AUTHOR=Gerratana Lorenzo , Basile Debora , Franzoni Alessandra , Allegri Lorenzo , Viotto Davide , Corvaja Carla , Bortot Lucia , Bertoli Elisa , Buriolla Silvia , Targato Giada , Da Ros Lucia , Russo Stefania , Bonotto Marta , Belletti Barbara , Baldassarre Gustavo , Damante Giuseppe , Puglisi Fabio 

TITLE=Plasma-Based Longitudinal Evaluation of ESR1 Epigenetic Status in Hormone Receptor-Positive HER2-Negative Metastatic Breast Cancer

JOURNAL=Frontiers in Oncology

VOLUME=10

YEAR=2020

URL=https://www.frontiersin.org/journals/oncology/articles/10.3389/fonc.2020.550185

DOI=10.3389/fonc.2020.550185

ISSN=2234-943X

ABSTRACT=<sec><title>Background</title><p>Endocrine therapy (ET) is the mainstay of treatment for hormone receptor-positive human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer; however, adaptive mechanisms emerge in about 25–30% of cases through alterations in the estrogen receptor ligand-binding domain, with a consequent ligand-independent estrogen receptor activity. Epigenetic-mediated events are less known and potentially involved in alternative mechanisms of resistance. The aim of this study was to test the feasibility of <italic>estrogen receptor 1</italic> (<italic>ESR1</italic>) epigenetic characterization through liquid biopsy and to show its potential longitudinal application for an early ET sensitivity assessment.</p></sec><sec><title>Methods</title><p>A cohort of 49 women with hormone receptor-positive HER2-negative MBC was prospectively enrolled and characterized through circulating tumor DNA using methylation-specific droplet digital PCR (MS-ddPCR) before treatment start (BL) and after 3 months concomitantly with computed tomography (CT) scan restaging (EV1). <italic>ESR1</italic> epigenetic status was defined by assessing the methylation of its main promoters (promA and promB). The most established cell-free tumor DNA (ctDNA) factors associated with ET resistance [<italic>ESR1</italic> and phosphatidylinositol-4,5-bisphosphate 3-kinase, catalytic subunit alpha (<italic>PIK3CA</italic>) mutations] were assessed through next-generation sequencing. Associations were tested through Mann–Whitney <italic>U</italic> test, matched pairs variations through Wilcoxon signed rank test, and survival was analyzed by log-rank test.</p></sec><sec><title>Results</title><p>The ET backbone was mainly based on aromatase inhibitors (AIs) (70.83%) in association with CDK4/6 inhibitors (93.75%). Significantly lower promA levels at baseline were observed in patients with liver metastases (<italic>P</italic> = 0.0212) and in patients with <italic>ESR1</italic> mutations (<italic>P</italic> = 0.0091). No significant impact on PFS was observed for promA (<italic>P</italic> = 0.3777) and promB (<italic>P</italic> = 0.7455) dichotomized at the median while a ≥2-fold increase in promB or in either promA or promB at EV1 resulted in a significantly worse prognosis (respectively <italic>P</italic> = 0.0189, <italic>P</italic> = 0.0294). A significant increase at EV1 was observed for promB among patients with <italic>PIK3CA</italic> mutation (<italic>P</italic> = 0.0173). A trend was observed for promB in <italic>ESR1</italic> wild-type patients and for promA in the <italic>ESR1</italic> mutant subgroup.</p></sec><sec><title>Conclusion</title><p>The study proofed the concept of an epigenetic characterization strategy based on ctDNA and is capable of being integrated in the current clinical workflow to give useful insights on treatment sensitivity.</p></sec>