A Study to See Whether Estrogen Can Slow the Growth of Some ER Positive Breast Cancers

Some breast cancers have estrogen receptors (ER+). The investigators know that some ER+ tumours can be cured by hormone therapy alone while other ER+ breast cancers cannot. Currently, there is no perfect way to tell these groups apart nor do the investigators know why some respond when others do not. Research findings suggest that the two types of ER+ breast cancers differ in their response to estrogen with estrogen being toxic to one type and not the other. For those tumours that find estrogen toxic, this may explain why tumours only start to grow when estrogen levels decrease after menopause. The purpose of this study is to see whether a two-week treatment of estrogen equal to pre-menopausal estrogen levels will decrease the rate at which patients' ER+ tumours grow. This will be done by comparing the growth rate in the tissue removed during standard of care surgery after patients have been treated with 7-14 days of estrogen prior to that surgery.

NCT Number	NCT02238808
Lead Sponsor	AHS Cancer Control Alberta
Conditions	Estrogen Receptor Positive Breast Cancer
Enrollment	19 participants
Start Date	2015-08
Primary Completion	2018-07-30 (estimated)
Study Completion	2028-06 (estimated)
Updated on ClinicalTrials.gov	2025-06-26