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.

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.