A Pre-operative Window Study of Letrozole Plus PR Agonist (Megestrol Acetate) Versus Letrozole Alone in Post-menopausal Patients With ER-positive Breast Cancer

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    Cambridge University Hospitals NHS Foundation Trust
Updated on 9 December 2022
endocrine therapy
hormone therapy
advanced breast cancer
progesterone receptor
aromatase inhibitor
estrogen receptor
breast adenocarcinoma
core needle biopsy
invasive carcinoma


Around 75% of breast cancers are defined and driven by Oestrogen receptor alpha (ER) transcriptional activity. Standard treatment is endocrine therapy however clinical outcomes vary considerably, and a proportion of women with early breast cancer driven by ER transcriptional activity develop drug resistance, and relapse with incurable, metastatic disease.

Historically, PR-positivity was viewed as just a passive consequence of a functional oestrogen receptor, and PR was established as a biomarker of ER functionality in breast cancer. However, recent preclinical discoveries have provided an alternative explanation to the previous over-simplistic assumption, providing new insights into progestogen action and functional 'cross-talk' between ER and PR in breast cancer. In the presence of agonist ligands, progesterone-activated PR causes rapid sequestration of ERa chromatin binding sites in breast cancer cells, resulting in a unique gene expression program that is associated with a good clinical outcomes. This highlights a potential therapeutic opportunity.

The PIONEER trial will investigate the effect of combining megestrol acetate (a progesterone receptor agonist) and letrozole (an aromatase inhibitor) in post menopausal women with early breast cancer. This is a 'window of opportunity' study treating and observing patients in the two weeks prior to definitive surgery. Patients are randomised into one of three arms; one in which the patients receive Letrozole alone; one in which they will receive a combination of Letrozole and low dose Megestrol acetate and the third arm will receive Letrozole and high dose Megestrol acetate. This trial will be open to postmenopausal women with newly diagnosed, untreated ER-positive, HER2-negative, invasive primary breast cancer.

Condition Breast Cancer, Breast Cancer, Breast Cancer Diagnosis, breast carcinoma, cancer, breast
Treatment Letrozole, Megestrol Acetate 40 MG, Megestrol Acetate 160 MG
Clinical Study IdentifierNCT03306472
SponsorCambridge University Hospitals NHS Foundation Trust
Last Modified on9 December 2022

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