A phase 1b study evaluating the effect of elacestrant treatment on estrogen receptor availability and estradiol binding

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RESEARCH ARTICLE

Open Access

A phase 1b study evaluating the effect of elacestrant treatment on estrogen receptor availability and estradiol binding to the estrogen receptor in metastatic breast cancer lesions using 18F-FES PET/CT imaging Agnes Jager1, Elisabeth G. E. de Vries2, C. Willemien Menke-van der Houven van Oordt3, Patrick Neven4, Clasina M. Venema2, Andor W. J. M. Glaudemans2, Yamei Wang5, Rebecca G. Bagley5, Maureen G. Conlan5* Philippe Aftimos6

and

Abstract Background: Elacestrant is an oral selective estrogen receptor (ER) degrader. This phase 1b open-label, nonrandomized study (RAD1901-106) was initiated to determine the effect of elacestrant on the availability of ER in lesions from postmenopausal women with ER+ advanced breast cancer (ABC) using 16α-18F-fluoro-17β-estradiol positron emission tomography with low-dose computed tomography (FES-PET/CT). Methods: Eligible patients were postmenopausal women with ER+, HER2− ABC; tumor progression after ≥ 6 months of 1–3 lines of endocrine treatment for ABC; and measurable or evaluable disease. Two 8-patient cohorts were enrolled: one treated with 400 mg elacestrant once daily (QD) and one treated with 200 mg elacestrant QD with dose escalation to 400 mg QD after 14 days. Elacestrant was dosed continuously until progressive disease, toxicity, or withdrawal. FES-PET/CT was performed pre-dose at baseline and 4 h post-dose on day 14. The primary endpoint was the percentage difference in FES uptake in tumor lesions (maximum 20) after 14 days of treatment compared to baseline. Overall response was investigator-assessed by Response Evaluation Criteria in Solid Tumors [RECIST] version 1.1. (Continued on next page)

* Correspondence: [email protected] 5 Radius Health, Inc., 950 Winter Street, Waltham, MA 02451, USA Full list of author information is available at the end of the article © The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.

Jager et al. Breast Cancer Research

(2020) 22:97

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