A Phase 3 Randomized, Open-Label Study of OP-1250 Monotherapy vs Standard of Care for the Treatment of ER+, HER2- Advanced or Metastatic Breast Cancer Following Endocrine and CDK 4/6 Inhibitor Therapy (OPERA-01)


This is an international, multicenter, randomized, open-label, active-controlled, phase 3 clinical trial. The purpose of this trial is to compare the safety and efficacy of palazestrant (OP-1250) as a single agent to the standard of care endocrine therapy: either fulvestrant or an aromatase inhibitor (anastrozole, letrozole, or exemestane). This trial is seeking adult participants with ER+, HER2- advanced or metastatic breast cancer whose disease has relapsed or progressed on 1 or 2 prior lines of standard-of-care endocrine therapy for metastatic breast cancer. Prior lines of therapy must include at least one line of endocrine therapy in combination with a CDK 4/6 inhibitor. In the dose-selection part of the trial, approximately 120 participants will be randomized to one of the two doses of palazestrant or to the standard-of-care endocrine therapy. Thereafter, approximately 390 participants will be randomized to palazestrant at the selected dose or to the standard-of-care endocrine therapy.


Accepting new patients

Primary Study Objective(s)

  • Dose-Selection Part: Incidence of adverse events
  • Dose-Selection Part: Incidence of dose reduction
  • Dose-Selection Part: Incidence of drug discontinuation
  • Trial: Progression-Free Survival (PFS)

Core eligibility

Note: This is only a partial list of eligibility criteria.

Key inclusion criteria:

  • Adult female or male participants.
  • ER+, HER2- locally advanced or metastatic breast cancer that is not amenable to curative therapy.
  • Evaluable disease (measurable disease or bone-only disease).
  • Previously received a CDK4/6 inhibitor in combination with an endocrine therapy in the advanced setting. One additional line of ET as a monotherapy is allowed. Duration of the most recent prior ET must be at least 6 months.
  • Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.
  • Adequate hematologic, hepatic, and renal functions.
  • Female participants can be pre-, peri- or postmenopausal.
  • Male and pre- or peri-menopausal female participants must be willing to take a GnRH (or LHRH) agonist.

Key exclusion criteria:

  • Symptomatic visceral disease, imminent organ failure, or any disease burden that makes the participant ineligible for endocrine therapy.
  • Previously received chemotherapy in the advanced/metastatic setting.
  • Previously received treatment with elacestrant or an investigational estrogen receptor-directed therapy.
  • History of allergic reactions to study treatment.
  • Any contraindications to the selected standard-of-care endocrine therapy in the local prescribing information.
  • Symptomatic central nervous system metastases, carcinomatous meningitis, leptomeningeal disease, or a spinal cord compression that require immediate treatment.
  • Clinically significant comorbidities such as significant cardiac or cerebrovascular disease, gastrointestinal disorders that could affect absorption of study treatment.