A Study to Evaluate the Safety, Pharmacokinetics, and Activity of GDC-0587 as a Monotherapy and in Combination With Giredestrant in Participants With Locally Advanced or Metastatic Estrogen Receptor-Positive and Human Epidermal Growth Factor Receptor 2-Negative (ER+/HER2-) Breast Cancer

June 1, 2026 updated by: Genentech, Inc.

A Phase Ia/Ib Dose-Escalation and Expansion Study Evaluating the Safety, Pharmacokinetics, and Activity of GDC-0587 as a Monotherapy and in Combination With Giredestrant in Patients With Locally Advanced Or Metastatic ER-Positive, HER2-Negative Breast Cancer Who Have Previously Progressed During or After CDK4/6 Inhibitor Therapy

This is a first-in-human, Phase Ia/Ib, dose-escalation and expansion study evaluating the safety, pharmacokinetics, and activity of GDC-0587 (cyclin-dependent kinase-4 [CDK4] inhibitor) as a monotherapy and in combination with giredestrant in participants with locally advanced or metastatic estrogen receptor-positive and human epidermal growth factor receptor 2-negative (ER+/HER2-) breast cancer who have previously progressed during or after CDK 4/6 inhibitor therapy.

Study Overview

Status

Status

Indicates the current recruitment status or the expanded access status.
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 (Estimated)

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.
136

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 Contact

Study Contact

The name and contact information for the person who can answer enrollment questions for a clinical study. Each location where the study is being conducted may also have a specific contact, who may be better able to answer those questions.

Study Contact Backup

  • Name: Fastest response: use the inquiry form. No email attachments. https://www.gene.com/contact-us/submit-medical-inquiry

Study Locations

  • Taiwan
      • Tainan, Taiwan, 70403
        • Recruiting
        • National Cheng Kung University Hospital
    • Taipei City
      • Taipei, Taipei City, Taiwan, 10002
        • Recruiting
        • National Taiwan University Hospital
  • United States
    • Michigan
      • Grand Rapids, Michigan, United States, 49546-7062
        • Recruiting
        • START - Midwest - EDOS
    • Texas
      • San Antonio, Texas, United States, 78229-3307
        • Recruiting
        • START - San Antonio - EDOS

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

  • Adult
  • Older Adult

Accepts Healthy Volunteers

No

Description

Inclusion Criteria:

  • Agreement to adhere to the contraception requirements
  • For females of childbearing potential ≤60 years of age and males: treatment with luteinizing hormone-releasing hormone (LHRH) agonist therapy beginning at least 2 weeks prior to Cycle 1, Day 1 and agreement to continue LHRH agonist therapy for the duration of the study
  • Histologically or cytologically confirmed adenocarcinoma of the breast that is locally advanced or metastatic
  • Previously documented ER+ and HER2- tumor according to American Society of Clinical Oncology (ASCO)/ College of American Pathologists (CAP) or European Society of Medical Oncology (ESMO) guidelines or any national guidelines with criteria conforming to ASCO/CAP or ESMO guidelines
  • Disease progression during or following treatment with an approved CDK 4/6 inhibitor, with or without endocrine therapy, in the locally advanced or metastatic setting
  • Measurable, or non-measurable but evaluable, disease per RECIST v1.1
  • Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1
  • Life expectancy ≥6 months
  • Creatinine clearance ≥60 milliliter per minute (mL/min) (calculated through use of the Cockcroft-Gault formula)

Exclusion Criteria:

  • Pregnant or breastfeeding, or intention of becoming pregnant during the study
  • Advanced, symptomatic, visceral spread that is at risk of life-threatening complications in the short term appropriate for treatment with cytotoxic chemotherapy at time of entry into the study, as per national or local treatment guidelines
  • Five or more prior lines of systemic therapy in the locally advanced or metastatic setting
  • Treatment with anti-cancer therapies, including investigational therapies, within 28 days or 5 drug elimination half-lives, whichever is shorter, prior to initiation of study drug
  • Treatment with an approved oral endocrine therapy within 7 days prior to initiation of study drug or treatment with fulvestrant or an approved/investigational CDK inhibitor within 21 days prior to initiation of study drug
  • History of Grade ≥3 adverse event attributed to prior CDK inhibitor therapy that resulted in permanent discontinuation of prior CDK inhibitor therapy
  • Poor peripheral venous access
  • Malabsorption condition or other gastrointestinal (GI) conditions/surgeries that the investigator assesses may significantly interfere with enteral absorption
  • Major surgical procedure within 28 days prior to initiation of study drug
  • Untreated, active CNS metastases
  • Infection requiring systemic (i.e., oral, IV, or intramuscular) antibiotics, chronic infection requiring treatment within 1 year prior to screening, or any evidence of current infection
  • History of malignancy within 3 years prior to screening, except for cancer under investigation in this study
  • Known history of a clinically significant abnormal ECG

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: Non-Randomized
  • 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: Phase Ia: GDC-0587 Monotherapy
Participants will receive GDC-0587 orally.
Drug: GDC-0587
Participants will receive GDC-0587 orally as per the schedule in the protocol.
Other Names:
  • RO7840736
  • RGT-587
Experimental: Phase Ib: GDC-0587 + Giredestrant Cohort
Participants will receive GDC-0587 and Giredestrant orally.
Drug: GDC-0587
Participants will receive GDC-0587 orally as per the schedule in the protocol.
Other Names:
  • RO7840736
  • RGT-587
Drug: Giredestrant
Participants will receive Giredestrant orally as per the schedule in the protocol.
Other Names:
  • GDC-9545
  • RO7197597
  • RG6171
Experimental: Phase Ib: GDC-0587 + Giredestrant Food-Effect and PPI-Effect Cohort
Participants will receive GDC-0587 and Giredestrant orally and also receive omeprazole for evaluating the effects of a proton pump inhibitor (PPI) and food on GDC-0587.
Drug: GDC-0587
Participants will receive GDC-0587 orally as per the schedule in the protocol.
Other Names:
  • RO7840736
  • RGT-587
Drug: Giredestrant
Participants will receive Giredestrant orally as per the schedule in the protocol.
Other Names:
  • GDC-9545
  • RO7197597
  • RG6171
Drug: Omeprazole
Participants will receive Omeprazole orally as per the schedule in the protocol.

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
Percentage of Participants with Adverse Events
Time Frame: From Baseline to 30 days after final dose of study treatment (Up to approximately to 18 months)
Measured by reporting the incidence and severity using the National Cancer Institute Common Terminology Criteria for Adverse Events (NCI CTCAE) v5.0 grading scale.
From Baseline to 30 days after final dose of study treatment (Up to approximately to 18 months)
Percentage of Participants with Dose-limiting Toxicity (DLTs)
Time Frame: Phase 1a: Days 1-28 of Cycle 1; Phase 1b: Days 1-28 of Cycle 1 (Each cycle is 28 days)
Phase 1a: Days 1-28 of Cycle 1; Phase 1b: Days 1-28 of Cycle 1 (Each cycle is 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
Time Frame
Percentage of Participants With Objective Response Rate (ORR) of Complete Response (CR) or Partial Response (PR) According to Response Evaluation Criteria in Solid Tumors Version 1.1 (RECIST v1.1)
Time Frame: Up to approximately to 18 months
Up to approximately to 18 months
Plasma Concentration of GDC-0587 as a Monotherapy and in Combination With Giredestrant
Time Frame: Phase 1a: Cycle 1 (Day 1, 2 15, 16), Cycle 2, 3, 5, 7, 9, 11 (Day 1); Phase 1b: Cycle 1 (Day 1, 2 15, 16), Cycle 2, 3, 5, 7, 9, 11 (Day 1) (Each cycle is 28 days)
Phase 1a: Cycle 1 (Day 1, 2 15, 16), Cycle 2, 3, 5, 7, 9, 11 (Day 1); Phase 1b: Cycle 1 (Day 1, 2 15, 16), Cycle 2, 3, 5, 7, 9, 11 (Day 1) (Each cycle is 28 days)
Plasma Concentration of GDC-0587 with Giredestrant Under Fasted and Fed Conditions
Time Frame: Part 1b: Cycle 1 (Day 1, 2, 4), Cycle 2, 3, 5, 7, 9 and 11 (Day 1) (Each cycle is 28 days)
Part 1b: Cycle 1 (Day 1, 2, 4), Cycle 2, 3, 5, 7, 9 and 11 (Day 1) (Each cycle is 28 days)
Plasma Concentration of GDC-0587 with Giredestrant Following Multiple-dose Administration, Either Alone or in Combination With Omeprazole
Time Frame: Part 1b: Cycle 1 (Day 11, 12, 20 and 21) (Each cycle is 28 days)
Part 1b: Cycle 1 (Day 11, 12, 20 and 21) (Each cycle is 28 days)
Recommended Phase II Dose (RP2D) of GDC-0587
Time Frame: Up to approximately to 18 months
Up to approximately to 18 months
Recommended Phase II Dose (RP2D) of GDC-0587 in Combination with Giredestrant
Time Frame: Up to approximately to 18 months
Up to approximately to 18 months

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.
Genentech, Inc.

Investigators

Investigators

A researcher involved in a clinical study. Related terms include site principal investigator, site sub-investigator, study chair, study director, and study principal investigator.
  • Study Director: Clinical Trials, Genentech, 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.

Helpful Links

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.
January 13, 2026

Primary Completion (Estimated)

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.
June 1, 2030

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.
June 1, 2030

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).
October 3, 2025

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.
October 3, 2025

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.
October 9, 2025

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.
June 3, 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.
June 1, 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.
June 1, 2026

More Information

Terms related to this study

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.
  • GO46057

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

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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