Pre-operative hormone therapy with and without Prometrium for early-stage breast cancer in postmenopausal women

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

Phase 2 Interventional St Vincent's Hospital · NCT03906669

This study is testing whether adding a natural hormone called Prometrium to standard breast cancer treatments helps postmenopausal women with early-stage hormone receptor positive breast cancer before their surgery.

Quick facts

PhasePhase 2
Study typeInterventional
Enrollment200 (estimated)
Ages18 Years and up
SexFemale
SponsorSt Vincent's Hospital Academic / other
Locations1 site (Sydney, New South Wales)
Trial IDNCT03906669 on ClinicalTrials.gov

What this trial studies

This phase II randomized, open-label study investigates the effects of pre-operative endocrine therapy in postmenopausal women with early-stage hormone receptor positive (HR+) and HER2-negative breast cancer. Participants will be randomly assigned to receive either letrozole alone, letrozole with Prometrium, or tamoxifen with Prometrium for 14 days before surgery. The study aims to explore the potential additive anti-cancer effects of combining natural progesterone with standard endocrine therapies. The research will involve 200 eligible women and will assess the impact of these treatments on tumor characteristics prior to definitive surgery.

Who should consider this trial

Good fit: Ideal candidates are postmenopausal women aged 18 and older with early-stage ER+, PR+, HER2-negative breast cancer.

Not a fit: Patients with locally advanced or inflammatory breast cancer, or those currently on hormone therapies, may not benefit from this study.

Why it matters

Potential benefit: If successful, this study could enhance the effectiveness of pre-operative treatments for early-stage breast cancer, potentially improving patient outcomes.

How similar studies have performed: While the specific combination of treatments in this study is novel, previous studies have shown promising results with similar approaches in hormone receptor positive breast cancer.

Eligibility criteria

Show full inclusion / exclusion criteria
Inclusion Criteria:

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

Exclusion Criteria:

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

Where this trial is running

Sydney, New South Wales

Study contacts

How to participate

  1. Review the eligibility criteria above with your treating physician.
  2. Visit the official trial page on ClinicalTrials.gov for the most current contact information and recruitment status.
  3. Contact the listed study coordinator or principal investigator to request pre-screening. Pre-screening is free and never obligates you to enroll.
Conditions Early-stage Breast CancerHormone Receptor Positive Tumorearly stage breast cancerprometriumprogesteronepost-menopausalendocrine therapy
Last reviewed 2026-06-13 by the Find a Trial editorial team. Information on this page is for educational purposes and is not medical advice. Always consult qualified healthcare professionals about clinical trial participation.