Study of Imlunestrant in Premenopausal Women with ER+ HER2- Early Breast Cancer

Inclusion Criteria

Cohort 1:

• Diagnosed with Stage I to III ER+ HER2- invasive breast cancer with a specific cell growth marker (Ki-67) of at least 10%.
• Willing to provide tumor samples before and during treatment.
• Have a good performance status, meaning fully active or restricted in physically strenuous activity but ambulatory.
• Able to swallow pills.
• Be premenopausal women.
• Use a highly effective non-hormonal birth control method if capable of becoming pregnant.
• Have good organ function.

Cohort 2:

• Diagnosed with early-stage ER+ HER2- breast cancer that has been surgically removed and has not spread.
• Completed local treatment for the cancer.
• Received at least 4.5 years of hormone therapy after surgery, or at least 2 years without additional ovarian suppression planned.
• Have a good performance status.
• Able to swallow pills.
• Be premenopausal women.
• Use a highly effective non-hormonal birth control method if capable of becoming pregnant.
• Have good organ function.

Exclusion Criteria

Cohort 1:

• Have certain types of breast cancer, such as bilateral invasive or inflammatory breast cancer.
• Have had both ovaries removed or treated to stop functioning.
• Have a serious medical condition.
• Had major surgery within the last 28 days.
• Have a history of other cancers unless in remission for at least 1 year.
• Plan to receive other cancer treatments not part of the study.
• Have had previous treatment for breast cancer.
• Have had radiation to the same side of the chest for any cancer.
• Have used anti-estrogen therapy before.
• Have used hormone therapy affecting the ovaries in the last year.
• Currently using hormone therapy for reproduction.

Cohort 2:

• Have ovarian cysts larger than 1 cm.
• Have certain types of breast cancer, such as metastatic or inflammatory breast cancer.
• Have had both ovaries removed or treated to stop functioning.
• Have a serious medical condition.
• Had major surgery within the last 28 days.
• Have a history of other cancers unless in remission for at least 1 year.
• Finished or stopped hormone therapy more than 6 months ago.
• Have used certain estrogen receptor-targeting drugs before.
• Currently using hormone therapy for reproduction.