A Phase I Dose Escalation and Dose Expansion and Phase II Monotherapy Open-label, First-in-Human, Multicenter Study of OP-1250 in Adult Subjects with Advanced and/or Metastatic Hormone Receptor (HR)-positive, HER2-negative Breast Cancer

This clinical trial is a Phase I dose escalation and dose expansion and Phase II monotherapy
open-label, first-in-human, multicenter study of OP-1250 in adult subjects with advanced
and/or metastatic hormone receptor (HR)-positive, her2-negative breast cancer.

Inclusion Criteria:

- Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1

- Must have received at least 1 prior hormonal regimen and at least 6 months of a prior
continuous endocrine therapy for locally advanced or metastatic disease

- Must not have received prior oral endocrine therapy < 2 weeks prior to first dose

- Must not have received prior, chemotherapy in 2 weeks or within 5 half-lives whichever
is earlier, antibody therapy within 4 weeks or investigational therapy within 4 weeks
or 5 half-lives whichever is earlier, prior to the first dose

- Adequate hepatic function

- Adequate renal function

- Normal coagulation panel

- Willingness to use effective contraception

Exclusion Criteria:

- Gastrointestinal disease

- Significant renal disease

- Significant cardiovascular disease

- Significant ECG abnormalities

- Ongoing systemic bacterial, fungal, or viral infection (requiring antimicrobial
therapy)

- Pregnancy or breastfeeding