A Study to Evaluate the Effect of GDC-4198 Alone and in Combination With Giredestrant Versus Abemaciclib and Giredestrant in Participants With Locally Advanced or Metastatic Estrogen Receptor-Positive (ER+), Human Epidermal Growth Factor Receptor-Negative (HER2-) Breast Cancer

Genentech

Status and phase: Enrolling; Phase 2; Phase 1

Conditions: Breast Cancer

Treatments: Drug: Giredestrant; Drug: Abemaciclib; Drug: GDC-4198

Study type: Interventional

Funder types: Industry; Other

Identifiers

NCT07100106

2025-521128-31-00 (EU Trial (CTIS) Number)

GO46021

Details and patient eligibility

About

The purpose of this study is to assess the safety of GDC-4198 alone and in combination with giredestrant and also the efficacy of GDC-4198 + giredestrant versus abemaciclib + giredestrant in participants with locally advanced or metastatic ER+, HER2- breast cancer. The study consists of 2 phases: Phase Ib and Phase II. Phase Ib will evaluate the safety and pharmacokinetics (PK) of GDC-4198 alone and in combination with giredestrant. Phase II stage will compare the activity and safety of GDC-4198 and giredestrant with abemaciclib and giredestrant.

Enrollment: 285 estimated patients

Sex: All

Ages: 18+ years old

Volunteers: No Healthy Volunteers

Inclusion criteria

• Histologically and/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 after treatment with an approved cyclin-dependent kinase 4/6 (CDK4/6) inhibitor and endocrine therapy (ET) in the locally advanced or metastatic setting.
• Measurable or non-measurable evaluable, disease per Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST v1.1)
• Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1
• Life expectancy ≥ 6 months

Exclusion criteria

• 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.
• Have received more than one-line of therapy for locally advanced or metastatic disease.
• Have received prior chemotherapy for metastatic breast cancer
• 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 (ET) within 7 days prior to initiation of study drug; treatment with fulvestrant or an approved CDK4/6 inhibitor within 21 days prior to initiation of study drug.
• Poor peripheral venous access
• Malabsorption condition or other gastrointestinal (GI) conditions/surgeries that the investigator assesses may significantly interfere with enteral absorption
• History of malignancy within 3 years prior to screening, except for cancer under investigation in this study and malignancies with a negligible risk of metastasis or death.

Trial design

Primary purpose: Treatment

Allocation: Randomized

Interventional model: Sequential Assignment

Masking: None (Open label)

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285 participants in 4 patient groups

Phase Ib: Dose-Finding Stage

Experimental group

Description:

Participants will receive GDC-4198 as monotherapy and in combination with giredestrant, 30 milligrams (mg), orally, daily, as per a pre-defined dosing regimen during each cycle until unacceptable toxicity or disease progression and/or loss of clinical benefit. (1 cycle=28 days).

Treatment:

Drug: GDC-4198

Drug: Giredestrant

Phase II: Arm A

Experimental group

Description:

Participants will receive GDC-4198, higher dose, in combination with giredestrant, 30 mg, orally, daily, as per a pre-defined dosing regimen during each cycle until unacceptable toxicity or disease progression and/or loss of clinical benefit. (1 cycle=28 days).

Treatment:

Drug: GDC-4198

Drug: Giredestrant

Phase II: Arm B

Experimental group

Description:

Participants will receive GDC-4198, lower dose, in combination with giredestrant, 30 mg, orally, daily, as per a pre-defined dosing regimen during each cycle until unacceptable toxicity or disease progression and/or loss of clinical benefit. (1 cycle=28 days).

Treatment:

Drug: GDC-4198

Drug: Giredestrant

Phase II: Arm C

Experimental group

Description:

Participants will receive abemaciclib, 150 mg twice daily, in combination with giredestrant, 30 mg, orally, daily, as per a pre-defined dosing regimen during each cycle until unacceptable toxicity or disease progression and/or loss of clinical benefit. (1 cycle=28 days).

Treatment:

Drug: Abemaciclib

Drug: Giredestrant