Abstract OT-09-05: A randomized, pre-surgical study to investigate the biological effects of AZD9833 doses in women with ER-positive HER2-negative primary breast cancer (SERENA-3)
Authors: Robertson John FR , Moppett Iain , Rocha Juan Enrique Bargalló , Dzagnidze Giorgi , Harding Joanna , Klinowska Teresa , Mather Richard , Mathewson Alastair , Maudsley Rhiannon , Morrow Christopher J , Saunders Andrew , Sykes Andy , Zhang Li , Lindemann Justin PO 
Published: February 2021

Abstract
Background AZD9833 is an orally bioavailable selective estrogen receptor (ER) antagonist and degrader (SERD) that has shown anti-tumor efficacy in a range of preclinical breast cancer models. SERENA-1, an ongoing first-in-human study assessing AZD9833 as a monotherapy and in combination with palbociclib, established dose-dependent tolerability in pre- and post-menopausal women at doses of 25-450 mg once daily (QD), with clinical benefit and target engagement at all dose levels. Two randomized, open-label Phase 2 trials are also ongoing in women with ER+ HER2- breast cancer. SERENA-2 compares the efficacy of AZD9833 with fulvestrant in post-menopausal women with advanced breast cancer following treatment with ≤1 endocrine therapy. SERENA-3 will examine the biological effects of different doses of AZD9833 in treatment-naïve women with primary breast cancer. Methods SERENA-3 is a randomized, open-label, parallel-group, pre-surgical study to investigate the biological effects of different doses of AZD9833 in ER+, HER2- primary breast cancer. Eligible patients will be post-menopausal (and potentially pre-menopausal) women awaiting curative-intent surgery for newly diagnosed, ER+ HER2- primary breast cancer. The study is designed in two stages. In Stage 1, 24 post-menopausal women will be randomized 1:1 to receive either 75 mg or 150 mg oral AZD9833 QD for 5-7 days, followed by a minimum 5-day pre-surgery washout period; Stage 2 gives provision for additional groups depending on emerging data from Stage 1. The primary objective of this study is to explore the effect of AZD9833 on ER expression in pre- and on-treatment tumor samples from women with primary breast cancer, as assessed by immunohistochemistry and H-score. Safety and tolerability will be assessed as secondary endpoints, along with the pharmacokinetic and pharmacodynamic effects of AZD9833 on other biomarkers. Blood will be collected at screening, on the day of biopsy and the day of surgery to assess circulating tumor DNA and exploratory biomarkers. Primary endpoint analysis will be performed on the pharmacodynamic analysis set. The study will be conducted in 20 centers across 3 countries. For more information please contact Professor John Robertson at: john.robertson@nottingham.ac.uk.
Citation Format: John FR Robertson, Iain Moppett, Juan Enrique Bargalló Rocha, Giorgi Dzagnidze, Joanna Harding, Teresa Klinowska, Richard Mather, Alastair Mathewson, Rhiannon Maudsley, Christopher J Morrow, Andrew Saunders, Andy Sykes, Li Zhang, Justin PO Lindemann. A randomized, pre-surgical study to investigate the biological effects of AZD9833 doses in women with ER-positive HER2-negative primary breast cancer (SERENA-3) [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr OT-09-05.