A Study of LY3484356 in Women With Breast Cancer Before Having Surgery

Inclusion Criteria:

Have histologically confirmed invasive ER+, HER2- breast carcinoma
Be willing and able to provide pre- and on-treatment tumor samples
Have a performance status of 0 or 1 on the Eastern Cooperative Oncology Group scale
Have adequate organ function
Be able to swallow capsules
Be a postmenopausal woman

Exclusion Criteria:

Have bilateral invasive breast cancer
Have metastatic breast cancer
Plan to receive concurrent neoadjuvant therapy with any other non-protocol anti-cancer therapy
Have had prior therapy (of any kind) for an invasive or non-invasive breast cancer
Have had prior radiotherapy to the ipsilateral chest wall for any malignancy
Have had prior anti-estrogen therapy with raloxifene, tamoxifen, aromatase inhibitor, or other selective estrogen receptor modulator (SERM), either for osteoporosis or prevention of breast cancer
Have had prior hormone-replacement therapy within 4 weeks of the start of study treatment
Have had major surgery within 28 days prior to randomization to allow for post-operative healing of the surgical wound and site(s)
Have certain infections such as hepatitis or tuberculosis or HIV that are not well controlled
Have another serious medical condition
Have a history of any other cancer (except nonmelanoma skin cancer or carcinoma in-situ of the cervix), unless in complete remission with no therapy for a minimum of 3 years