Combination of estradiol and olaparib for advanced breast cancer treatment

Phase 1b Study of Olaparib and Estradiol in Advanced ER+ Breast Cancer (PHOEBE)

Phase 1 Interventional Dartmouth-Hitchcock Medical Center · NCT05900895

This study is testing a new treatment combining estradiol and olaparib to see if it helps post-menopausal women with advanced breast cancer that hasn't responded to other therapies.

Quick facts

PhasePhase 1
Study typeInterventional
Enrollment6 (estimated)
Ages18 Years and up
SexFemale
SponsorDartmouth-Hitchcock Medical Center Academic / other
Drugs / interventionsdenosumab, chemotherapy, radiation
Locations1 site (Lebanon, New Hampshire)
Trial IDNCT05900895 on ClinicalTrials.gov

What this trial studies

This clinical trial aims to evaluate the safety and optimal dosage of olaparib when combined with 17b-estradiol in post-menopausal women suffering from advanced ER+/HER2- breast cancer. Participants will receive the combination treatment for two cycles, followed by single-agent estradiol until disease progression occurs. The study will assess clinical benefits, progression-free survival, objective response rates, tumor metabolic response, and any associated toxicities. This approach targets patients with endocrine-resistant breast cancer who have previously undergone endocrine therapy.

Who should consider this trial

Good fit: Ideal candidates include post-menopausal women with ER+/HER2- metastatic or locally advanced breast cancer who have previously received endocrine therapy.

Not a fit: Patients with known CNS disease, recent history of certain cardiovascular events, or those currently undergoing other anti-cancer therapies may not benefit from this study.

Why it matters

Potential benefit: If successful, this treatment could provide a new therapeutic option for patients with advanced breast cancer who have limited treatment alternatives.

How similar studies have performed: While the combination of estradiol and olaparib is a novel approach, similar studies have shown promise in targeting endocrine-resistant breast cancer.

Eligibility criteria

Show full inclusion / exclusion criteria
Inclusion Criteria:

* Post-menopausal women with ER+/HER2- breast cancer.
* Metastatic or locoregional recurrence not amenable to treatment with curative intent.
* Received ≥1 prior line of endocrine-based therapy in the advanced/metastatic setting.

Exclusion Criteria:

* During study treatment, no concurrent anti-cancer therapies are allowed with the following exceptions:

  o Anti-resorptive bone therapies (e.g., bisphosphonates, denosumab) permitted.
* Any investigational cancer therapy or systemic chemotherapy in the last 3 weeks.
* Any radiation therapy in the last 2 weeks.
* Known CNS disease, unless clinically stable for ≥ 3 months.
* Concomitant use of known strong or moderate CYP3A inhibitors.
* Persistent toxicities (≥CTCAE grade 2) caused by previous cancer therapy.
* History of any of the following:

  * Deep venous thrombosis
  * Pulmonary embolism
  * Stroke
  * Acute myocardial infarction
  * Congestive heart failure
  * Previous malignancy not treated with curative intent, or with an estimated recurrence risk ≥30%
  * Severe renal impairment (creatinine clearance ≤ 30 mL/min).

Where this trial is running

Lebanon, New Hampshire

Study contacts

How to participate

  1. Review the eligibility criteria above with your treating physician.
  2. Visit the official trial page on ClinicalTrials.gov for the most current contact information and recruitment status.
  3. Contact the listed study coordinator or principal investigator to request pre-screening. Pre-screening is free and never obligates you to enroll.
Conditions Metastatic Breast Cancermetastaticlocally advancedestradiol therapyolaparib
Last reviewed 2026-06-13 by the Find a Trial editorial team. Information on this page is for educational purposes and is not medical advice. Always consult qualified healthcare professionals about clinical trial participation.