A Phase 1b Study of Aurora A Kinase Inhibitor LY3295668 erbumine in Monotherapy and Combination Therapy in Patients with Metastatic Breast Cancer post CDK4/6 Inhibitor and Endocrine Therapy

The reason for this study is to determine the recommended phase 2 dose of the study drug
LY3295668 erbumine in participants with breast cancer that has spread to other parts of the
body.

Inclusion Criteria:

- Participant must have hormone receptor positive and HER2 negative metastatic breast
cancer

- Participant must have progressed on at least 1 line of endocrine therapy and 1 cyclin
dependent kinase (CDK)4/6 inhibitor

- Participant must be able and willing to undergo mandatory tumor biopsy

- Participant must have normal organ function

- Participant must be able to swallow capsules

Exclusion Criteria:

- Participant must not have had prior chemotherapy for mBC. Chemotherapy in the
adjuvant/neoadjuvant setting is permitted

- Participant must not be currently enrolled in a clinical study

- Participant must not have another serious medical condition

- Participant must not have previously received an aurora kinase inhibitor