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



The primary purpose of phase 1 portion of this study is to determine the maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D) of H3B-6545 in women with locally advanced or metastatic estrogen receptor (ER)-positive, human epidermal growth factor 2 (HER2)-negative breast cancer.

The primary purpose of phase 2 portion of this study 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 1-2 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 (or subsequent amendments) must have received prior cyclin-dependent kinase (CDK4/6) inhibitor therapy. Up to one prior chemotherapy in the metastatic setting is allowed.
  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 (or subsequent amendments) must have measurable disease at baseline as per Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 criteria.
  8. Participants under amendment 6 (or subsequent amendments) must have ESR1 Y537S mutation in absence of ESR1 D538G mutation as per the results of a central laboratory from a Nucleic Acids Whole Blood sample.

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.


  • UCSF
    San Francisco California 94158 United States
  • University of California Los Angeles
    Los Angeles California 90404 United States


in progress, not accepting new patients
Start Date
Completion Date
Eisai Inc.
Phase 1/2 research study
Study Type
About 206 people participating
Last Updated