for females ages 18 years and up (full criteria)
at San Francisco, California and other locations
study started
estimated completion



The purpose of phase 1 is to determine safety, tolerability and pharmacokinetics (PK) of H3B-6545 in women with locally advanced or metastatic estrogen receptor (ER)-positive, human epidermal growth factor 2 (HER2)-negative breast cancer. The purpose of phase 2 is to estimate the efficacy of H3B-6545 in terms of best overall response rate, duration of response (DoR), clinical benefit rate (CBR), disease control rate (DCR), progression-free survival (PFS), and overall survival (OS) in all participants with ER-positive, HER2-negative breast cancer and in those with and without ER alpha mutation [including a clonal estrogen receptor 1 gene (ESR1) Y537S mutation].

Official Title

A Phase I-II Multicenter, Open Label Trial of H3B-6545, a Covalent Antagonist of Estrogen Receptor Alpha, in Women With Locally Advanced or Metastatic Estrogen Receptor-positive, HER2 Negative Breast Cancer


Breast Neoplasms Breast Cancer Estrogen-receptor Positive Breast Cancer Cancer, Breast Breast Cancer Female Breast Adenocarcinoma Estrogen Receptor Positive Tumor ER Positive estrogen receptor H3B-6545 Endocrine Therapy


You can join if…

Open to females ages 18 years and up

  1. Pre- or post-menopausal women.
  2. ER-positive, HER2-negative breast cancer that is advanced or metastatic.
  3. Progressed on prior therapy. Multiple prior lines of therapy allowed in Phase 1 and 2. Participants under amendment 6 must have received prior cyclin-dependent kinase (CDK4/6) inhibitor therapy.
  4. A recent archival tumor tissue obtained within 6 months prior to enrollment or a fresh tumor biopsy must be provided. A second biopsy after initiating trial therapy is not required.
  5. Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0 or 1.
  6. Adequate bone marrow and organ function.
  7. Participants under amendment 6 must have measurable disease at baseline as per Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 criteria.
  8. Participants under amendment 6 must have ESR1 Y537S mutation in absence of ESR1 D538G mutation as per the results of a central laboratory.

You CAN'T join if...

  1. Participants must have at least one measurable lesion.
  2. Participant with inflammatory breast cancer.
  3. Participant has received more than one prior chemotherapy regimen for metastatic disease (Phase 2 only).
  4. Females of childbearing potential who are unable or unwilling to follow adequate contraceptive measures.


  • University of California San Francisco accepting new patients
    San Francisco California 94158 United States
  • University of California Los Angeles accepting new patients
    Los Angeles California 90404 United States


accepting new patients
Start Date
Completion Date
H3 Biomedicine Inc.
Phase 1/2
Study Type
Last Updated