This is a Phase 1/2, open-label, multicenter, dose-escalation and expansion study to evaluate
the safety, tolerability, pharmacokinetics, and preliminary efficacy of ZN-c5 administered
orally in subjects with advanced estrogen receptor positive, human epidermal growth factor
receptor 2 negative (ER+/HER2-) breast cancer. ZN-c5 will be evaluated both as monotherapy
and in combination with palbociclib (IBRANCE®).