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

The film gives the main points. The full list below is copied from the registry; the study team makes the final decision.

• Age18 Years to no maximum
• SexFemale
• Healthy volunteersNo

You may be able to join if

• 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.

You cannot join if

• Cohort 1:
• Have bilateral invasive metastatic, occult primary, or inflammatory breast cancer.
• Have had prior bilateral oophorectomy or ovarian ablation.
• Have a serious medical condition
• Had major surgery within 28 days prior to randomization.
• Have a history of other cancer (except non melanoma skin cancer, Stage I uterine cancer, or carcinoma in situ of the cervix or other in situ cancer), unless in complete remission with no therapy for a minimum of 1 year.
• Plan to receive concurrent neoadjuvant therapy with any other non-protocol anticancer therapy.
• Have had any prior therapy for an invasive or non-invasive breast cancer.
• Have had prior radiotherapy to the ipsilateral chest wall for any malignancy.
• Have received prior anti-estrogen therapy, including for osteoporosis or prevention of breast cancer.
• Have had prior treatment with any Gonadotropin-releasing hormone (GnRH) agonist within 12 months prior to randomization.
• Receiving current exogenous reproductive hormone therapy
• Cohort 2:
• Have ovarian cyst(s) greater than (>) 1 centimeter (cm) at screening.
• Have metastatic occult primary, or inflammatory breast cancer.
• Have had prior bilateral oophorectomy or ovarian ablation.
• Have a serious medical condition
• Had major surgery within 28 days prior to randomization.
• Have a history of other cancer (except non melanoma skin cancer or carcinoma in situ of the cervix or other in situ cancer), unless in complete remission with no therapy for a minimum of 1 year.
• Completed or discontinued prior adjuvant ET >6 months prior to screening.
• Have received prior therapy with any selective estrogen receptor degrader (SERD).
• Receiving current exogenous reproductive hormone therapy.

This is how the treatment is meant to work. Whether it helps, and how safe it is, is what this trial is testing.

imlunestrant. An orally available selective estrogen receptor degrader (SERD), with potential antineoplastic activity. Upon oral administration, imlunestrant specifically targets and binds to the estrogen receptor (ER) and induces a conformational change that results in ER degradation. This prevents ER-mediated signaling and inhibits both the growth and survival of ER-expressing cancer cells. NCI Drug Dictionary

Treatments listed in the registry

• Imlunestrant (Drug): Given orally
• Goserelin (Drug): Given SC
• Tamoxifen 20 mg (Drug): Given orally

Randomized · Parallel · masking: None

Main goals

• Change from Baseline in Antigen Kiel (Ki-67) Expression (Baseline, Day 29)
• Rate of Symptomatic Ovarian Cysts (Up to Day 180)

Other goals

• Change from Baseline in Estrogen Receptor (ER) Expression
• Change from Baseline in Progesterone Receptor (PR) Expression
• Rate of Complex Ovarian Cysts

Planned enrollment: 600 (estimated).

• Indiana University Melvin and Bren Simon Cancer Center, Indianapolis, Indiana
• New York Cancer and Blood Specialists, Shirley, New York
• Tennessee Oncology, Nashville, Tennessee
• University of Texas MD Anderson Cancer Center, Houston, Texas
• Oncology Consultants P.A., Houston, Texas
• Inova Schar Cancer Institute, Fairfax, Virginia

7 recruiting sites outside the US. Site status as of Oct 30, 2026. Check the live record before contacting a site.

• ClinicalTrials.gov NCT07287098
• NCI Drug Dictionary: C174042

Registry record reviewed as fetched Oct 30, 2026, last updated by the sponsor Oct 7, 2026. Public record; not medical advice.