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-protocolanti-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, aromataseinhibitor, or other selective estrogen receptor modulator (SERM), either forosteoporosis or prevention of breast cancer

• Have had prior hormone-replacement therapy within 4 weeks of the start of studytreatment

• Have had major surgery within 28 days prior to randomization to allow forpost-operative healing of the surgical wound and site(s)

• Have certain infections such as hepatitis or tuberculosis or HIV that are not wellcontrolled

• Have another serious medical condition

• Have a history of any other cancer (except nonmelanoma skin cancer or carcinomain-situ of the cervix), unless in complete remission with no therapy for a minimumof 3 years