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

What this study is about

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 join (things the study team will check)

✅ You may be able to join if…

• 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 may not be able to join if…

• 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.

Where this trial is running

• University of Alabama at Birmingham, Birmingham, Alabama, United States
• Ironwood Cancer & Research Centers, Chandler, Arizona, United States
• USC/Norris Comprehensive Cancer Center, Los Angeles, California, United States
• UCLA Hematology/Oncology - Parkside, Santa Monica, California, United States
• Banner MD Anderson Cancer Center at North Colorado Medical Center, Greeley, Colorado, United States
• Banner MD Anderson Cancer Center at McKee Medical Center, Loveland, Colorado, United States
• AdventHealth Altamonte Springs, Altamonte Springs, Florida, United States
• Winship Cancer Institute, Atlanta, Georgia, United States
• Indiana University Melvin and Bren Simon Cancer Center, Indianapolis, Indiana, United States
• University of Kentucky Chandler Medical Center, Lexington, Kentucky, United States
• Massachusetts General Hospital, Boston, Massachusetts, United States
• Dana-Farber Cancer Institute, Boston, Massachusetts, United States

+ 62 more sites.

Who to contact

Trial questions or participation questions: 1-877-CTLILLY (1-877-285-4559) or · 1-317-615-4559 · LillyTrials@Lilly.com

It's completely normal to call and ask questions before deciding anything. Mention the study ID: NCT07287098.