Abstract OT2-01-10: WinPro: A window of opportunity study of endocrine therapy with and without prometrium in postmenopausal women with early-stage hormone receptor-positive breast cancer
Authors: Downton Teesha , Segara Davendra , Ong Andrew , Bingham Janne , Carson Emma-Kate , Chen Julia , Middleton Kate , Lindeman Geoffrey , Parker Andrew , Lim Elgene 
Published: March 2023

WinPro: A window of opportunity study of endocrine therapy with and without prometrium in postmenopausal women with early-stage hormone receptor-positive breast cancer Authors Teesha Downton1,2,3, Davendra Segara3, Andrew Ong4, Janne Bingham5, Emma-Kate Carson4, Julia Chen1,2,3, Kate Middleton3, Geoffrey Lindeman6, Andrew Parker3, Elgene Lim1,2,3. Affiliations 1Garvan Institute of Medical Research, Darlinghurst NSW, Australia; 2School of Clinical Medicine, St Vincent’s Healthcare Clinical Campus, Faculty of Medicine and Health, University of New South Wales Sydney, Australia; 3St Vincent’s Hospital Sydney, Darlinghurst NSW, Australia; 4Campbelltown Hospital, Campbelltown NSW, Australia; 5Royal Adelaide Hospital, Adelaide SA, Australia; 6Walter & Eliza Hall Institute of Medical Research, Parkville VIC, Australia Disclosures T. Downton: None. D. Segara: None. A. Ong: None. J. Bingham: None. E. Carson: None. J. Chen: None. K. Middleton: None. G. Lindeman: None. A. Parker: None. E. Lim: Advisory Board for Pfizer, Astra Zeneca, Lilly, Roche, Novartis, Gilead Australia. Research Funding from Pfizer, Novartis, Bayer. Abstract Background: Preclinical studies have observed that progesterone has inhibitory effects on the estrogen-stimulated growth of estrogen receptor (ER)-positive, progesterone receptor (PR)-positive breast cancer. Mohammed H et al. (Nature 2015) identified that activated PR associates with the ER and modulates the interactions of the ER with chromatin, with a shift towards the transcription of genes associated with apoptosis and differentiation, and away from genes associated with proliferation. We hypothesize that the addition of prometrium, a microionized progesterone, may enhance the anti-proliferative effects of standard endocrine therapy in women with ER-positive PR-positive breast cancer. Trial Design: WinPro (NCT03906669) is an ongoing multicenter, phase II, randomized, open-label, window of opportunity study comparing the effect on standard endocrine therapy with or without prometrium on breast cancer cell proliferation. The study population is postmenopausal women with early-stage operable breast cancer where the tumor is ≥5mm on imaging, ER ≥10%, PR≥10%, and HER2-negative. Patients currently on hormone replacement therapy or the oral contraceptive pill, or who have a history of endometrial cancer or venous thromboembolism are not eligible. Patients are randomized 1:1:1 to letrozole 2.5mg daily, letrozole 2.5mg + prometrium 300mg daily, or tamoxifen 20mg + prometrium 300mg daily. Allocated treatment is taken for 14 days prior to surgery. Primary surgery and adjuvant treatment is as per standard of care. Objectives: The primary objective is to compare the geometric mean suppression of centrally assessed Ki67 between the diagnostic biopsy sample (pre-treatment) and the surgical sample (post-treatment). The secondary objective is to evaluate safety and tolerability. Tertiary objectives include defining genes predictive of a reduction in Ki67, and evaluating the changes in ER, PR, AR, FoxA1, Cyclin D1, and apoptotic markers in breast tumors post-intervention. Accrual: This study opened in February 2018 and as of 13 July 2022, 164 patients have been enrolled. Target accrual is 200 patients. Contact information: This study is led at St Vincent’s Hospital Sydney, Australia, and funded by the Cancer Council of NSW and the NHMRC Translational Breast Cancer Project grant. Contact: Elgene Lim MBBS FRACP PhD at e.lim@garvan.org.au.

Citation Format: Teesha Downton, Davendra Segara, Andrew Ong, Janne Bingham, Emma-Kate Carson, Julia Chen, Kate Middleton, Geoffrey Lindeman, Andrew Parker, Elgene Lim. WinPro: A window of opportunity study of endocrine therapy with and without prometrium in postmenopausal women with early-stage hormone receptor-positive breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr OT2-01-10.