Giredestrant / Abemaciclib / GDC-4198 · Phase 1/2 Trial

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

ClinicalTrials.gov · August 10, 2026

Preliminary Why this matters to you Expert discussion

Early or partial results. Treat as a signal, not a conclusion.

AI Summary

This is an active, ongoing Phase 1b/2 trial comparing a novel agent GDC-4198 alone and in combination with giredestrant against abemaciclib plus giredestrant in advanced ER+/HER2− breast cancer. No outcome data are available in this registry record; results are not yet reported.

What was studied

Phase 1/2, Interventional, Randomized, Sequential, Open label, Treatment purpose. Breast Cancer; age from 18 Years. Intervention: Phase Ib: Dose-Finding Stage; Phase II: Arm A; Phase II: Arm B; Phase II: Arm C. Compared with: Abemaciclib in combination with giredestrant (Phase 2 only). n = 285. 61 sites across 10 countries.

Key findings

Safety

Safety was not reported in the material analysed. Check the source before drawing any conclusion about harm.

Who this may help

The source did not state who this applies to in practice.

Plain-language summary

This is a Phase 1b/2 trial registration with no results posted; the study is actively recruiting and designed to evaluate safety and efficacy of a novel agent in combination therapy for ER+/HER2− breast cancer.

Study design

As stated by the source record.

MethodsPrimary outcome measures: Phase Ib: Incidence and Severity of Adverse Events (AEs) (assessed at Up to 36 months); Phase Ib: Number of Participants With Dose-Limiting Toxicity (DLTs) (assessed at From Day 1 to Day 28 of Cycle 1 (1 cycle=28 days)); Phase II: Progression-free Survival (PFS) (assessed at Up to 36 months)

DesignPhase 1/2, Interventional, Randomized, Sequential, Open label, Treatment purpose

PopulationBreast Cancer; age from 18 Years

Sample size285

InterventionPhase Ib: Dose-Finding Stage; Phase II: Arm A; Phase II: Arm B; Phase II: Arm C

ComparatorAbemaciclib in combination with giredestrant (Phase 2 only)

Setting61 sites across 10 countries

Reported figures

Quoted from the source exactly as published.

Planned enrollment285

Phase Ib primary outcomeIncidence and Severity of Adverse Events, up to 36 months

Phase Ib primary outcomeNumber of Participants With Dose-Limiting Toxicity, Day 1 to Day 28 of Cycle 1

Phase II primary outcomeProgression-free Survival, up to 36 months

Caveats

No results are posted in this registry record; study is currently recruiting.
Blinding status, randomization method, and dose/schedule details for GDC-4198 are not described in the registry text.
Phase 1b and Phase 2 enrollment split is not specified.
Comparator arm details (abemaciclib + giredestrant dosing and schedule) not provided in registry text.

Evidence assessment

Graded across the dimensions that decide whether you should act, each from what the source actually supports. There is no single score, and where a dimension was not assessed it says so.

Study design

moderate

Phase 1b/2 design with safety and efficacy endpoints; Phase 2 includes active comparator arm.

Directness

strong

Directly addresses locally advanced or metastatic ER+/HER2− breast cancer; Phase 2 includes comparative arm.

Consistency

insufficient

No results posted; consistency cannot be assessed against other evidence.

Risk of bias

insufficient

Registry record only; blinding, allocation concealment, and conduct details not reported.

Sample adequacy

moderate

Estimated 285 participants across Phase 1b and 2; Phase 2 PFS comparison powered but exact allocation unclear.

What is missing. This record has no key findings. That is a gap in the analysis, not a judgement about the study.

Source abstract

Registry record from ClinicalTrials.gov (NCT07100106). This is a study registration, not published results. Lead sponsor: Genentech, Inc.. Recruitment status: RECRUITING. Phase: PHASE1, PHASE2. Study type: INTERVENTIONAL. Enrollment: 285 participants (ESTIMATED). Conditions: Breast Cancer. Interventions: DRUG: GDC-4198; DRUG: Giredestrant; DRUG: Abemaciclib. Primary outcome measures: Phase Ib: Incidence and Severity of Adverse Events (AEs) , Up to 36 months; Phase Ib: Number of Participants With Dose-Limiting Toxicity (DLTs) , From Day 1 to Day 28 of Cycle 1 (1 cycle=28 days); Phase II: Progression-free Survival (PFS) , Up to 36 months. Brief summary: 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.

Follow from this

Taken from the source record, never inferred. Follow any of these and new work involving them reaches your briefing.

GiredestrantGenentechNCT07100106AbemaciclibGDC-4198Breast Cancer