Not Yet RecruitingPhase 2

A Study of Imlunestrant (LY3484356) in Premenopausal Women With Estrogen Receptor-Positive (ER+) Human Epidermal Growth Factor Receptor 2 Negative (HER2-) Early Breast Cancer

United States600 participantsStarted 2026-05

Plain-language summary

This study will include two groups of patients: Cohort 1 and Cohort 2. Cohort 1: will help researchers learn how a medicine called imlunestrant (LY3484356) affects a specific type of breast cancer. Some patients will take both imlunestrant and another treatment to suppress their ovarian function. Some will take it without ovarian suppression. Researchers will compare the effects in breast cancer cells to those of another medicine called tamoxifen. All patients in this group will be premenopausal women who have a type of early breast cancer called estrogen receptor-positive, HER2-negative. The treatment in this group will last for up to 29 days. Cohort 2: will help researchers understand how imlunestrant affects the ovaries when it is taken without ovarian suppression. Researchers will compare the effects to those of another medicine called tamoxifen. This group will also include premenopausal women with the same type of breast cancer. The treatment in this group will last for up to 6 months.

Who can participate

Age range18 Years

SexFEMALE

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AI-rewrites the medical criteria so a patient or caregiver can understand them. Always confirm with the trial site.

Inclusion Criteria: Cohort 1: * Have histologically confirmed Stage I to III Estrogen Receptor positive (ER+), human epidermal growth factor receptor 2 negative (HER2-) invasive breast carcinoma with Ki-67 at least 10% * Be willing and able to provide pre- and on-treatment tumor samples. * Have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1. * Be able to swallow capsules or tablets. * Be premenopausal women. * If of childbearing potential must use 1 highly effective method of non-hormonal contraception while receiving study treatment and for the duration specified in protocol. * Have adequate organ function. Cohort 2: * Have a diagnosis of ER+, HER2- early-stage, resected, invasive breast cancer without evidence of distant metastasis * Have undergone definitive loco-regional therapy. * Have received at least 4.5 years of any adjuvant endocrine therapy (ET), or at least 2 years of adjuvant ET with no additional ovarian suppression planned. * Have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1. * Be able to swallow capsules or tablets. * Be premenopausal women * If of childbearing potential must use 1 highly effective method of non-hormonal contraception while receiving study treatment and for the duration specified in protocol. * Have adequate organ function. Exclusion Criteria: Cohort 1: * Have bilateral invasive metastatic, occult primary, or inflammatory breast cancer. * Have had prior bilateral oophorectomy or ov…

What they're measuring

Change from Baseline in Antigen Kiel (Ki-67) Expression

Timeframe: Baseline, Day 29

Rate of Symptomatic Ovarian Cysts

Timeframe: Up to Day 180

Trial details

NCT IDNCT07287098

SponsorEli Lilly and Company

Sponsor typeINDUSTRY

Study typeINTERVENTIONAL

Primary completion2029-01

Contact for this trial

Trial questions or participation questions: 1-877-CTLILLY (1-877-285-4559) or

1-317-615-4559 LillyTrials@Lilly.com