A Study of H3B-6545 in Combination With Palbociclib in Women With Advanced or Metastatic Estrogen Receptor-Positive Human Epidermal Growth Factor Receptor-2 (HER2)-Negative Breast Cancer

February 16, 2026 updated by: Eisai Inc.

An Open-Label Multicenter Phase 1b Study of H3B-6545 in Combination With Palbociclib in Women With Advanced or Metastatic Estrogen Receptor-Positive HER2-Negative Breast Cancer

The primary objective of this study is to evaluate the safety and tolerability of H3B-6545 and palbociclib when administered in combination in order to determine the maximum tolerated dose (MTD) and/or the recommended Phase 2 dose (RP2D) of this combination in women with advanced or metastatic estrogen receptor-positive (ER+) HER2- breast cancer.

Study Overview

Status

Status

Indicates the current recruitment status or the expanded access status.
Active, not recruiting

Conditions

Conditions

The disease, disorder, syndrome, illness, or injury that is being studied. On ClinicalTrials.gov, conditions may also include other health-related issues, such as lifespan, quality of life, and health risks.

Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.

Study Type

Study Type

Describes the nature of a clinical study. Study types include interventional studies (also called clinical trials), observational studies (including patient registries), and expanded access.
Interventional

Enrollment (Actual)

Enrollment

The number of participants in a clinical study. The "anticipated" enrollment is the target number of participants that the researchers need for the study.
31

Phase

Phase

The stage of a clinical trial studying a drug or biological product, based on definitions developed by the U.S. Food and Drug Administration (FDA). The phase is based on the study's objective, the number of participants, and other characteristics. There are five phases: Early Phase 1 (formerly listed as Phase 0), Phase 1, Phase 2, Phase 3, and Phase 4. Not Applicable is used to describe trials without FDA-defined phases, including trials of devices or behavioral interventions.
  • Phase 1

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

  • United Kingdom
      • London, United Kingdom
        • Royal Marsden NHS Foundation Trust
      • London, United Kingdom
        • Sarah Cannon Research Institute UK - SCRI
      • Sutton, United Kingdom
        • Royal Marsden NHS Foundation Trust
  • United States
    • Florida
      • Sarasota, Florida, United States, 34232
        • Florida Cancer Specialists South - SCRI - PPDS
    • Massachusetts
      • Boston, Massachusetts, United States, 02114
        • Massachusetts General Hospital
    • Missouri
      • Kansas City, Missouri, United States, 64111
        • Saint Luke's Cancer Institute
    • Nevada
      • Las Vegas, Nevada, United States, 89169
        • Comprehensive Cancer Centers of Nevada
    • Tennessee
      • Nashville, Tennessee, United States, 37203
        • Tennessee Oncology, PLLC - SCRI - PPDS

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Eligibility Criteria

The key requirements that people who want to participate in a clinical study must meet or the characteristics they must have. Eligibility criteria consist of both inclusion criteria (which are required for a person to participate in the study) and exclusion criteria (which prevent a person from participating). Types of eligibility criteria include whether a study accepts healthy volunteers, has age or age group requirements, or is limited by sex.

Ages Eligible for Study

18 years and older (Adult, Older Adult)

Accepts Healthy Volunteers

No

Description

Inclusion Criteria:

  1. ER+ HER2- locally advanced, recurrent, or metastatic breast cancer, as per local laboratory
  2. Prior therapy in the advanced/metastatic setting
  3. Has an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1
  4. Has adequate bone marrow and organ function

Exclusion Criteria:

  1. Uncontrolled significant active infections
  2. Major surgery or other locoregional treatment within 4 weeks before the 1st dose of study drug
  3. Inability to take oral medication or presence of malabsorption
  4. Active cardiac disease or a history of cardiac dysfunction
  5. Evidence of ongoing Alcohol or Drug Abuse

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Treatment
  • Allocation: N/A
  • Interventional Model: Sequential Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm

Participant Group / Arm

A group or subgroup of participants in a clinical trial that receives a specific intervention/treatment, or no intervention, according to the trial's protocol.
Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.
Experimental: Palbociclib + H3B-6545 (Dose Escalation and Dose Expansion)
Participants will receive Palbociclib 75, 100, 125 milligram (mg) capsules or tablets, orally, once daily from Days 1 to 21 followed by 7 days off treatment in 28-day cycles along with H3B-6545 150, 300, 450 mg capsules or tablets, orally, once daily from Days 1 to 28 in 28-day cycles in dose escalation part. Based on MTD or RP2D determined for H3B-6545 in combination with palbociclib in dose escalation part, participants will continue to receive study treatment in dose expansion part until PD, development of unacceptable toxicity, or withdrawal of consent (up to 24 months).
Drug: Palbociclib (75, 100, 125 milligram [mg])
Palbociclib orally, once daily (QD).
Drug: H3B-6545 (150, 300, 450 mg)
H3B-6545 orally, QD.

What is the study measuring?

Primary Outcome Measures

Primary Outcome Measures

In a clinical study's protocol, the planned outcome measure that is the most important for evaluating the effect of an intervention/treatment. Most clinical studies have one primary outcome measure, but some have more than one.
Outcome Measure
Measure Description
Time Frame
Maximum Tolerated Dose (MTD) of H3B-6545 and Palbociclib
Time Frame: Cycle 1 (Cycle length = 28 Days)
The MTD was defined as the highest dose at which no more than 1 of 6 participants experienced a Dose-Limiting Toxicity (DLT) in the dose cohort. DLT was graded as per National Cancer Institute (NCI) Common Terminology Criteria for Adverse Events (CTCAE) version 5.0. DLTs were defined as the following events that occurred in Cycle 1, for which a causal relationship with the study drug could not be ruled out: febrile neutropenia; Grade 4 neutropenia that was not resolved within 7 days; Grade 4 thrombocytopenia; Grade 3 thrombocytopenia lasting greater than (>) 7 days or associated with clinically significant bleeding; Grade 4 vomiting and diarrhea; Grade 3 vomiting and diarrhea lasting > 72 hours despite treatment; Grade 4 electrolyte abnormality or Grade 3 abnormality lasting > 24 hours; Grade 3 or 4 serum creatinine or bilirubin increase; Grade 4 biochemistry or Grade 3 lasting > 7 days; Grade 4 or Grade 3 or intolerable grade 2 toxicities of any non-hematologic adverse event.
Cycle 1 (Cycle length = 28 Days)

Secondary Outcome Measures

Secondary Outcome Measures

In a clinical study's protocol, a planned outcome measure that is not as important as the primary outcome measure for evaluating the effect of an intervention but is still of interest. Most clinical studies have more than one secondary outcome measure.
Outcome Measure
Measure Description
Time Frame
Number of Participants With Treatment-emergent Adverse Events (TEAEs) and Serious Adverse Events (SAEs)
Time Frame: From first dose up to 28 days after the last dose of study drug (up to Month 48)
TEAE was defined as an adverse event (AE) with an onset that had occurred after receiving study drug. An AE was defined as any untoward medical occurrence in a participants or clinical investigation participant administered an investigational product. An AE does not necessarily have a causal relationship with medicinal product. A serious adverse event (SAE) was defined as any AE if it resulted in death or life-threatening AE or required inpatient hospitalization or prolongation of existing hospitalization or resulted in persistent or significant incapacity or substantial disruption of the ability to conduct normal life functions or was a congenital anomaly/birth defect. Analysis is not final for this outcome measure, and complete data will be posted at study completion date.
From first dose up to 28 days after the last dose of study drug (up to Month 48)
AUC(0-t): Area Under the Plasma Concentration-time Curve From Time 0 to the Last Measurable Point for Palbociclib and H3B-6545
Time Frame: Dose Escalation Part: Cycle 1 Days 8, 21 and 28: 0-24 hours postdose; Dose Expansion Part: Cycle 1 Day 21: 0-24 hours postdose (Each Cycle length=28 days)
Analysis is not final for this outcome measure, and complete data will be posted at study completion date.
Dose Escalation Part: Cycle 1 Days 8, 21 and 28: 0-24 hours postdose; Dose Expansion Part: Cycle 1 Day 21: 0-24 hours postdose (Each Cycle length=28 days)
Cmax: Maximum Observed Plasma Concentration for Palbociclib and H3B-6545
Time Frame: Dose Escalation Part: Cycle 1 Days 8, 21 and 28: 0-24 hours postdose; Dose Expansion Part: Cycle 1 Day 21: 0-24 hours postdose (Each Cycle length=28 days)
Analysis is not final for this outcome measure, and complete data will be posted at study completion date.
Dose Escalation Part: Cycle 1 Days 8, 21 and 28: 0-24 hours postdose; Dose Expansion Part: Cycle 1 Day 21: 0-24 hours postdose (Each Cycle length=28 days)
Tmax: Time to Reach the Cmax for Palbociclib and H3B-6545
Time Frame: Dose Escalation Part: Cycle 1 Days 8, 21 and 28: 0-24 hours postdose; Dose Expansion Part: Cycle 1 Day 21: 0-24 hours postdose (Each Cycle length=28 days)
Analysis is not final for this outcome measure, and complete data will be posted at study completion date.
Dose Escalation Part: Cycle 1 Days 8, 21 and 28: 0-24 hours postdose; Dose Expansion Part: Cycle 1 Day 21: 0-24 hours postdose (Each Cycle length=28 days)
C24: Plasma Concentration at 24 Hour Post-dose for Palbociclib and H3B-6545
Time Frame: Dose Escalation Part: Cycle 1 Days 8, 21 and 28: 0-24 hours postdose; Dose Expansion Part: Cycle 1 Day 21: 0-24 hours postdose (Each Cycle length=28 days)
Analysis is not final for this outcome measure, and complete data will be posted at study completion date.
Dose Escalation Part: Cycle 1 Days 8, 21 and 28: 0-24 hours postdose; Dose Expansion Part: Cycle 1 Day 21: 0-24 hours postdose (Each Cycle length=28 days)
Ratio of Pharmacokinetic (PK) Cmax Parameter Estimates Between Day 21 (Palbociclib) and Day 8 (Palbociclib)
Time Frame: Dose Escalation Part: Cycle 1 Days 8 and 21: 0-24 hours postdose
Ratio of palbociclib Cmax Day 21/Day 8, is the ratio of palbociclib exposure on Day 21 and palbociclib exposure on Day 8. Analysis is not final for this outcome measure, and complete data will be posted at study completion date.
Dose Escalation Part: Cycle 1 Days 8 and 21: 0-24 hours postdose
Ratio of PK AUC24 Parameter Estimates Between Day 21 (Palbociclib) and Day 8 (Palbociclib)
Time Frame: Dose Escalation Part: Cycle 1 Days 8 and 21: 0-24 hours postdose; Dose Expansion Part: Cycle 1 Day 21: 0-24 hours postdose (Each Cycle length=28 days)
Ratio of palbociclib AUC24 Day 21/Day 8, is the ratio of palbociclib exposure on Day 21 and palbociclib exposure on Day 8. Analysis is not final for this outcome measure, and complete data will be posted at study completion date.
Dose Escalation Part: Cycle 1 Days 8 and 21: 0-24 hours postdose; Dose Expansion Part: Cycle 1 Day 21: 0-24 hours postdose (Each Cycle length=28 days)
Ratio of PK C24 Parameter Estimates Between Day 21 (Palbociclib) and Day 8 (Palbociclib)
Time Frame: Dose Escalation Part: Cycle 1 Days 8 and 21: 0-24 hours postdose; Dose Expansion Part: Cycle 1 Day 21: 0-24 hours postdose (Each Cycle length=28 days)
Ratio of palbociclib C24 Day 21/Day 8, is the ratio of palbociclib exposure on Day 21 and palbociclib exposure on Day 8. Analysis is not final for this outcome measure, and complete data will be posted at study completion date.
Dose Escalation Part: Cycle 1 Days 8 and 21: 0-24 hours postdose; Dose Expansion Part: Cycle 1 Day 21: 0-24 hours postdose (Each Cycle length=28 days)
Ratio of PK Cmax Parameter Estimates Between Day 21 (H3B-6545) and Day 28 (H3B-6545)
Time Frame: Dose Escalation Part: Cycle 1 Days 21 and 28: 0-24 hours postdose; Dose Expansion Part: Cycle 1 Day 21: 0-24 hours postdose (Each Cycle length=28 days)
Ratio of palbociclib Cmax Day 21/Day 28, is the ratio of H3B-6545 exposure on Day 21 and H3B-6545 exposure on Day 28. Analysis is not final for this outcome measure, and complete data will be posted at study completion date.
Dose Escalation Part: Cycle 1 Days 21 and 28: 0-24 hours postdose; Dose Expansion Part: Cycle 1 Day 21: 0-24 hours postdose (Each Cycle length=28 days)
Ratio of PK AUC24 Parameter Estimates Between Day 21 (H3B-6545) and Day 28 (H3B-6545)
Time Frame: Dose Escalation Part: Cycle 1 Days 21 and 28: 0-24 hours postdose; Dose Expansion Part: Cycle 1 Day 21: 0-24 hours postdose (Each Cycle length=28 days)
Ratio of H3B-6545 AUC24 Day 21/Day 28, is the ratio of H3B-6545 exposure on Day 21 and H3B-6545 exposure on Day 28. Analysis is not final for this outcome measure, and complete data will be posted at study completion date.
Dose Escalation Part: Cycle 1 Days 21 and 28: 0-24 hours postdose; Dose Expansion Part: Cycle 1 Day 21: 0-24 hours postdose (Each Cycle length=28 days)
Ratio of PK C24 Parameter Estimates Between Day 21 (H3B-6545) and Day 28 (H3B-6545)
Time Frame: Dose Escalation Part: Cycle 1 Days 21 and 28: 0-24 hours postdose; Dose Expansion Part: Cycle 1 Day 21: 0-24 hours postdose (Each Cycle length=28 days)
Ratio of H3B-6545 C24 Day 21/Day 28, is the ratio of H3B-6545 exposure on Day 21 and H3B-6545 exposure on Day 28. Analysis is not final for this outcome measure, and complete data will be posted at study completion date.
Dose Escalation Part: Cycle 1 Days 21 and 28: 0-24 hours postdose; Dose Expansion Part: Cycle 1 Day 21: 0-24 hours postdose (Each Cycle length=28 days)
Objective Response Rate (ORR)
Time Frame: From first dose of study drug up to Month 48
ORR is defined as the percentage of participants achieving a best overall response (BOR) of confirmed partial response (PR) or complete response (CR). The ORR will be assessed according to Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1. Analysis is not final for this outcome measure, and complete data will be posted at study completion date.
From first dose of study drug up to Month 48
Duration of Response (DoR)
Time Frame: From the date of first documented CR/PR until the PD or death, whichever occurs first (up to Month 48)
DoR is defined as the time from the date of the first documented CR/PR until the first documentation of disease progression (PD) or death, whichever comes first. The DoR will be assessed according to RECIST version 1.1. Analysis is not final for this outcome measure, and complete data will be posted at study completion date.
From the date of first documented CR/PR until the PD or death, whichever occurs first (up to Month 48)
Clinical Benefit Rate (CBR)
Time Frame: From the first dose of study drug until disease progression or death, whichever occurs first (up to Month 48)
CBR is defined as the percentage of participants with BOR of PR, CR, or durable stable disease (SD) (duration of SD greater than or equal to 23 weeks). Duration of SD is defined as the time from the date of first dose to the date of the first documentation of disease progression or death, whichever occurs first. It will be calculated for participants whose BOR is SD. The CBR will be assessed according to RECIST version 1.1. Analysis is not final for this outcome measure, and complete data will be posted at study completion date.
From the first dose of study drug until disease progression or death, whichever occurs first (up to Month 48)
Progression-free Survival (PFS)
Time Frame: From first dose of study drug until first documentation of PD or death, whichever occurs first (up to Month 48)
PFS is defined as the time from the first dose date to the date of the first documentation of PD or death (whichever occurs first). Analysis is not final for this outcome measure, and complete data will be posted at study completion date.
From first dose of study drug until first documentation of PD or death, whichever occurs first (up to Month 48)
Overall Survival (OS)
Time Frame: From the date of first dose to the date of death from any cause (up to Month 48)
OS is defined as the time from first dose date to the date of death from any cause. Analysis is not final for this outcome measure, and complete data will be posted at study completion date.
From the date of first dose to the date of death from any cause (up to Month 48)

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Sponsor

The organization or person who initiates the study and who has authority and control over the study.
Eisai Inc.

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

Study Start

The actual date on which the first participant was enrolled in a clinical study. The "anticipated" study start date is the date that the researchers think will be the study start date.
April 1, 2020

Primary Completion (Actual)

Primary Completion

The date on which the last participant in a clinical study was examined or received an intervention to collect final data for the primary outcome measure. Whether the clinical study ended according to the protocol or was terminated does not affect this date. For clinical studies with more than one primary outcome measure with different completion dates, this term refers to the date on which data collection is completed for all the primary outcome measures. The "anticipated" primary completion date is the date that the researchers think will be the primary completion date for the study.
September 16, 2022

Study Completion (Estimated)

Study Completion

The date on which the last participant in a clinical study was examined or received an intervention/treatment to collect final data for the primary outcome measures, secondary outcome measures, and adverse events (that is, the last participant's last visit). The "anticipated" study completion date is the date that the researchers think will be the study completion date.
March 31, 2027

Study Registration Dates

First Submitted

First Submitted

The date on which the study sponsor or investigator first submitted a study record to ClinicalTrials.gov. There is typically a delay of a few days between the first submitted date and the record's availability on ClinicalTrials.gov (the first posted date).
February 26, 2020

First Submitted That Met QC Criteria

First Submitted That Met QC Criteria

The date on which the study sponsor or investigator first submits a study record that is consistent with National Library of Medicine (NLM) quality control (QC) review criteria. The sponsor or investigator may need to revise and submit a study record one or more times before NLM's QC review criteria are met. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
February 26, 2020

First Posted (Actual)

First Posted

The date on which the study record was first available on ClinicalTrials.gov after National Library of Medicine (NLM) quality control (QC) review has concluded. There is typically a delay of a few days between the date the study sponsor or investigator submitted the study record and the first posted date.
February 27, 2020

Study Record Updates

Last Update Posted (Actual)

Last Update Posted

The most recent date on which changes to a study record were made available on ClinicalTrials.gov. There may be a delay between when the changes were submitted to ClinicalTrials.gov by the study's sponsor or investigator (the last update submitted date) and the last update posted date.
February 27, 2026

Last Update Submitted That Met QC Criteria

Last Update Submitted That Met QC Criteria

The most recent date on which the study sponsor or investigator submitted changes to a study record that are consistent with National Library of Medicine (NLM) quality control (QC) review criteria. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
February 16, 2026

Last Verified

Last Verified

The most recent date on which the study sponsor or investigator confirmed the information about a clinical study on ClinicalTrials.gov as accurate and current. If a study with a recruitment status of recruiting; not yet recruiting; or active, not recruiting has not been confirmed within the past 2 years, the study's recruitment status is shown as unknown.
July 1, 2025

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

Other Study ID Numbers

Identifiers or ID numbers other than the NCT number that are assigned to a clinical study by the study's sponsor, funders, or others. These numbers may include unique identifiers from other trial registries and National Institutes of Health grant numbers.
  • H3B-6545-G000-102
  • 2019-004622-17 (EudraCT Number)

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

YES

IPD Plan Description

Eisai's data sharing commitment and further information on how to request data can be found on our website http://eisaiclinicaltrials.com/.

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

Yes

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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