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RecruitingLast updated: 5 February 2024

WinPro: This phase II trial is evaluating the effectiveness of delivering different combinations of hormone therapy (including letrozole, prometrium and tamoxifen) prior to surgery in postmenopausal women with early-stage breast cancerA Window of Opportunity Study of Endocrine Therapy With and Without Prometrium in Postmenopausal Women With Early Stage Hormone Receptor-positive Breast Cancer.

Clinical summary


This is a randomised, open label study recruiting postmenopausal women with early-stage ER+, PR+, HER-negative breast cancer. The trial has three arms, each running for 14 days. Participants will receive treatment after diagnosis but prior to surgery. In Arm 1, participants will receive letrozole 2.5mg, administered orally once daily. In Arm 2, participants will receive letrozole 2.5mg and prometrium 300mg, administered orally once daily. In Arm 3, participants will receive tamoxifen 20mg and prometrium 300mg, administered orally once daily.


This trial is treating patients with early stage ER+, PR+, HER-negative breast cancer


Breast Cancers Breast





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Trial sponsor

St. Vincent's Hospital-Manhattan

Scientific Title

A Window of Opportunity Study of Endocrine Therapy With and Without Prometrium in Postmenopausal Women With Early Stage Hormone Receptor-positive Breast Cancer.



  1. Histologically confirmed ER+ and PR+ breast cancer (defined as ≥10% positive staining cells)
  2. Histologically confirmed HER2-negative breast cancer (defined as IHC 0-1 and/or FISH/CISH <2.2)
  3. Tumour size ≥1 cm as measured by ultrasound and/or mammogram
  4. Ability to understand all patient information and informed-consent documents, written informed consent to participate in the trial, and to avail tissue and blood samples for research
  5. Aged 18 years or older


  1. Women currently on hormone therapies, including hormone replacement therapy and oral contraceptive pill
  2. Locally advanced/inoperable and inflammatory breast cancer
  3. Planned for a mastectomy (due to increased risk of venous thromboembolism)
  4. Clinical evidence of metastatic disease
  5. Patients treated with other preoperative systemic therapies
  6. Nut allergy (prometrium contains peanut oil)
  7. Prior history of uterine cancer, deep vein thrombosis, pulmonary embolism or clotting disorder
  8. Women who are pregnant or breast-feeding


  • You are able to swallow medication by mouth.


  • You have certain types of non-cancer medical conditions.
  • You have had certain treatments, surgical procedures or drugs.

Clinical trials have complex eligibility criteria.

Ask your doctor if this trial could be right for you.

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