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

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

doi:10.3389/fonc.2020.550185

Abstract

BackgroundEndocrine 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 estrogen receptor 1 (ESR1) epigenetic characterization through liquid biopsy and to show its potential longitudinal application for an early ET sensitivity assessment.MethodsA 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). ESR1 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 [ESR1 and phosphatidylinositol-4,5-bisphosphate 3-kinase, catalytic subunit alpha (PIK3CA) mutations] were assessed through next-generation sequencing. Associations were tested through Mann–Whitney U test, matched pairs variations through Wilcoxon signed rank test, and survival was analyzed by log-rank test.ResultsThe 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 (P = 0.0212) and in patients with ESR1 mutations (P = 0.0091). No significant impact on PFS was observed for promA (P = 0.3777) and promB (P = 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 P = 0.0189, P = 0.0294). A significant increase at EV1 was observed for promB among patients with PIK3CA mutation (P = 0.0173). A trend was observed for promB in ESR1 wild-type patients and for promA in the ESR1 mutant subgroup.ConclusionThe 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.

Highlights

Endocrine therapy (ET) is the mainstay of treatment for hormone receptorpositive human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer; adaptive mechanisms emerge in about 25–30% of cases through alterations in the estrogen receptor ligand-binding domain, with a consequent ligandindependent estrogen receptor activity
A cohort of 49 patients with luminal-like metastatic BC (MBC) treated with first-line ET was prospectively enrolled between May 2018 and November 2019
Of the 11 patients treated with a fulvestrant-based ET, 9 patients relapsed during adjuvant ET

Summary

Introduction

Endocrine therapy (ET) is the mainstay of treatment for hormone receptorpositive human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer; adaptive mechanisms emerge in about 25–30% of cases through alterations in the estrogen receptor ligand-binding domain, with a consequent ligandindependent estrogen receptor activity. As a matter of fact, ESR1 mutations are not often present in primary tumors but are rather selected during AI-based therapies and eventually characterize the dominant clone when disease progression occurs [10] Their onset is associated with a lower treatment benefit in subsequent lines when an AI-based backbone is selected, while discordant data are available with respect to SERDS [5, 11]. Several promoters are involved in ESR1’s tissue-specific regulation and in particular, two proximal promoters (promoter A and B) are located within ∼2 kb of the transcription start site and are transcriptionally active in BC [18,19,20]

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