(Z)-Endoxifen for Premenopausal ER+/HER2- Breast Cancer

This study is looking at (Z)-endoxifen as a potential treatment for premenopausal women with a specific type of breast cancer (ER+/HER2-). (Z)-endoxifen is a type of drug called a SERM, which helps block estrogen from attaching to cancer cells. You may be eligible if you are a woman aged 18 or older with this type of breast cancer, are not pregnant, and meet other criteria. The study aims to see how your body processes (Z)-endoxifen and if it can effectively reduce cancer cell growth or shrink tumors. Some participants will receive (Z)-endoxifen alone, while others will also receive goserelin, a drug that temporarily stops the ovaries from making estrogen. The current recruitment status is unclear.

Study design
This is an open-label study, meaning you and your doctors will know which treatment you are receiving. It plans to enroll about 87 participants and has two parts: one to study how the body processes the drug and another to evaluate its treatment effects.
What's involved
You will take (Z)-endoxifen capsules daily. Some participants will also receive a monthly injection of goserelin. The study will measure drug levels after 4 weeks and tumor response after 24 weeks.
Compensation
Not stated in the trial record.
Follow-up
The study will measure tumor response after 24 weeks of treatment.

AI-generated from the public study record. Only the study team can confirm whether you're eligible — confirm details with them before making decisions.

NCT05607004

(Z)-Endoxifen for the Treatment of Premenopausal Women With ER+/HER2- Breast Cancer

Active, Not Recruiting
PHASE2Ages 18+InterventionalTreatment
Atossa Therapeutics, Inc.
~87 participants
Updated 2026-07-08 on ClinicalTrials.gov
What's tested:(Z)-endoxifengoserelin

At a glance

Recruiting sites
0 of 14 listed sites are recruiting right now
RecruitingSuspended, closed, or not yet open
What they're measuring
PK Cohort - (Z)-endoxifen steady-state plasma concentrations
Measured over After 4 weeks of treatment
+2 more outcomes measured
Breast Neoplasms
Invasive Breast Cancer
Estrogen-receptor-positive Breast Cancer
HER2-negative Breast Cancer
14 sites across 13 states
Arizona2
California1
Florida1
Illinois1
Kentucky1
Michigan1
Minnesota1
Missouri1
  • Matthew P Goetz, MD · PRINCIPAL_INVESTIGATOR · Mayo Clinic

This trial hasn't published a contact. View it on ClinicalTrials.gov

  • PK Cohort - (Z)-endoxifen steady-state plasma concentrationsAfter 4 weeks of treatment

    (Z)-endoxifen steady-state plasma concentrations (Css) of evaluable subjects who completed at least one cycle of treatment (28 +/- 3 days)

  • For Analysis of Cohort A (Treatment Cohort): determine whether the week 4 Ki-67≤10% rate is at least 65%After 4 weeks of treatment

    For analysis Cohort A (subjects that have a baseline Ki-67\>10%): the primary objective is to determine whether the Week 4 Ki-67 ≤ 10% rate is at least 65% among premenopausal women with primary estrogen receptor positive (ER+), Human Epidermal Growth Factor Receptor 2 negative (HER2-) breast cancer.

  • For analysis Cohort B (Treatment Cohort): determine the objective tumor response rate at 24 weeksAfter 24 weeks of treatment

    For analysis Cohort B (subjects have baseline Ki-67≤ 10%): the primary objective is to determine the objective tumor response rate at 24 weeks among premenopausal women with ER+, HER2-, Ki-67 ≤ 10% breast cancer receiving (Z) endoxifen plus goserelin.