Trial of 4-Hydroxytamoxifen (4-OHT) Gel in Women Aimed at Reducing Dense Breast Tissue

This is a randomized, double blind, placebo-controlled study. Subjects will have been assessed as having mammographically dense breast (heterogeneously dense (C) or extremely dense (D), based on the American College of Radiology (ACR) Breast Imaging-Reporting and Data System (BIRADS©) fifth edition classification) for eligibility. Approximately 330 subjects will be enrolled at approximately 25 sites in the US and the European Union. Subjects who give informed consent will be stratified, based on whether they are pre/peri or post-menopausal and randomized 2:1 within those groups to receive either 8 mg/day (4 mg/breast) 4-OHT or matching placebo for up to 52 weeks. Subjects will apply the investigational gel to both breasts once per day until they have completed 52 weeks of study drug administration. There will be, in addition, an optional 52 weeks of open-label treatment for those subjects who choose to continue treatment. Subjects will capture daily gel administration in a diary to monitor compliance. While on treatment, subjects will return to the clinic for study assessments, a review of adverse events (AEs) and to re-supply study gel at 13, 26, 39, weeks and at 52 weeks for those subjects who have agreed to take part in the open-label phase of the study. During the study, in a case of significant changes in bleeding pattern or other signs/symptoms which could be related to endometrial pathology, the Investigator will perform a uterine ultrasound followed by an endometrial biopsy if indicated. Open-Label Treatment Phase Secondary Outcome Measures: • Comparison of breast density measurements (Cumulus and Volpara) • Laboratory parameters will be summarized in a descriptive fashion. • Incidence and severity of AEs will be compared between BHR-700 gel and placebo.