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