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GDC-9545

Phase 1

Breast Cancer | Small molecule | Oncology |Roche Holding AG|Last Updated: Aug 13, 2026

Success Probability

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Market & Valuation

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Trial Design

CONTROLLED
Total Trials1
Total Enrollment181

FDA Designations

No designations recorded

Clinical trial landscape

GDC-9545 · 1 trial · 1 indication

Phase 1 1
NCT03332797A Study of GDC-9545 Alone or in Combination With Palbociclib and/or Luteinizing Hormone-Releasing Hormone (LHRH) Agonist in Locally Advanced or Metastatic Estrogen Receptor-Positive Breast CancerBreast Cancer
ACTIVE NOT_RECRUITING181 Analytics
PHASE1ACTIVE NOT_RECRUITING
A Study of GDC-9545 Alone or in Combination With Palbociclib and/or Luteinizing Hormone-Releasing Hormone (LHRH) Agonist in Locally Advanced or Metastatic Estrogen Receptor-Positive Breast Cancer
Breast CancerUnlock trial analytics

Study Endpoints

Primary Endpoints

Number of Participants with Adverse Events by Severity, According to National Cancer Institute Common Terminology Criteria for Adverse Events version 4.0 (NCI-CTCAE v4.0)
From Baseline until 28 days after the last dose of study treatment (up to 84 months)
Dose Escalation: Maximum Tolerated Dose (MTD) or Maximum Administered Dose (MAD) of GDC-9545 When Administered as a Single Agent or in Combination with Palbociclib
Days -7 to 28 of Cycle 1
Dose Escalation: Number of Participants with Dose-Limiting Toxicities When GDC-9545 is Administered as a Single Agent or in Combination with Palbociclib
Days -7 to 28 of Cycle 1
Change from Baseline in Systolic Blood Pressure Over Time
Baseline and at each treatment cycle (1 cycle is 28 days) through to 28 days after the last dose of study treatment
Change from Baseline in Diastolic Blood Pressure Over Time
Baseline and at each treatment cycle (1 cycle is 28 days) through to 28 days after the last dose of study treatment
Change from Baseline in Body Temperature Over Time
Baseline and at each treatment cycle (1 cycle is 28 days) through to 28 days after the last dose of study treatment
Change from Baseline in Pulse Rate Over Time
Baseline and at each treatment cycle (1 cycle is 28 days) through to 28 days after the last dose of study treatment
Change from Baseline in Respiration Rate Over Time
Baseline and at each treatment cycle (1 cycle is 28 days) through to 28 days after the last dose of study treatment
Change from Baseline in Electrocardiogram (ECG) Results Over Time: Heart Rate
Baseline and at predefined intervals from Cycle 1 and at each subsequent cycle (1 cycle is 28 days) through to the last dose of study treatment
Change from Baseline in ECG Results Over Time: PR Duration
Baseline and at predefined intervals from Cycle 1 and at each subsequent cycle (1 cycle is 28 days) through to the last dose of study treatment
Change from Baseline in ECG Results Over Time: QRS Duration
Baseline and at predefined intervals from Cycle 1 and at each subsequent cycle (1 cycle is 28 days) through to the last dose of study treatment
Change from Baseline in ECG Results Over Time: QT Duration
Baseline and at predefined intervals from Cycle 1 and at each subsequent cycle (1 cycle is 28 days) through to the last dose of study treatment
Change from Baseline in ECG Results Over Time: QTcF Duration
Baseline and at predefined intervals from Cycle 1 and at each subsequent cycle (1 cycle is 28 days) through to the last dose of study treatment
Change from Baseline in ECG Results Over Time: RR Duration
Baseline and at predefined intervals from Cycle 1 and at each subsequent cycle (1 cycle is 28 days) through to the last dose of study treatment
Number of Participants with Clinical Laboratory Abnormalities in Hematology Tests by Highest Grade According to NCI-CTCAE v4.0
Baseline, Cycle 1, and at each subsequent cycle (1 cycle is 28 days) or at every other cycle starting from Cycle 3 (Cohort X only), up to 28 days after the last dose of study treatment

Laboratory parameters for hematology will be measured and compared with a standard reference range. Values outside of the standard reference range are considered abnormalities. Not every laboratory abnormality qualifies as an adverse event. A laboratory test result will be reported as an adverse event if it meets any of the following criteria: is accompanied by clinical symptoms; results in a change in study treatment, a medical intervention, or a change in concomitant therapy; or is clinically significant in the investigator's judgment.

Number of Participants with Clinical Laboratory Abnormalities in Blood Chemistry Tests by Highest Grade According to NCI-CTCAE v4.0
Baseline, Cycle 1, and at each subsequent cycle (1 cycle is 28 days) or at every other cycle starting from Cycle 3 (Cohort X only), up to 28 days after the last dose of study treatment

Laboratory parameters for blood chemistry will be measured and compared with a standard reference range. Values outside of the standard reference range are considered abnormalities. Not every laboratory abnormality qualifies as an adverse event. A laboratory test result will be reported as an adverse event if it meets any of the following criteria: is accompanied by clinical symptoms; results in a change in study treatment, a medical intervention, or a change in concomitant therapy; or is clinically significant in the investigator's judgment.

Number of Participants with Clinical Laboratory Abnormalities in Urinalysis Tests by Highest Grade According to NCI-CTCAE v4.0
Baseline, Cycle 3, and at every other cycle (1 cycle is 28 days) up to 28 days after the last dose of study treatment

Laboratory parameters for urinalysis will be measured and compared with a standard reference range. Values outside of the standard reference range are considered abnormalities. Not every laboratory abnormality qualifies as an adverse event. A laboratory test result will be reported as an adverse event if it meets any of the following criteria: is accompanied by clinical symptoms; results in a change in study treatment, a medical intervention, or a change in concomitant therapy; or is clinically significant in the investigator's judgment.

Secondary Endpoints

Plasma Concentration of GDC-9545 Over Time
At predefined intervals from Cycle 1, Day -7 (Single-Agent Dose Escalation and A1-A5 only) or Cycle 1, Day 1 (B0, B1, and B2) to Cycle 4, Day 1 (1 cycle is 28 days) and at study completion; Cycle 1, Days -7 or 8 (C1 only); Cycle 1, Day 8 (C2 only)
Plasma Concentration of Palbociclib Over Time
At predefined intervals from Cycle 1, Day 1 to Cycle 4, Day 1 (1 cycle is 28 days) and at study completion (B0, B1, and B2 only); Cycle 1, Day 8 (C2 only)
Plasma Concentration of LHRH Over Time
At predefined intervals from Cycle 1, Day 1 to Cycle 4, Day 1 (1 cycle is 28 days) and at study completion (B2 only)
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Study Design & Arms

AllocationNON_RANDOMIZED
MaskingNONE
ModelSEQUENTIAL
PurposeTREATMENT

Treatment Arms

ArmTypeDescription
Dose Escalation: GDC-9545EXPERIMENTALDuring dose escalation, postmenopausal participants will be assigned sequentially to escalating doses of GDC-9545, up to the maximum tolerated dose (MTD) or maximum administered dose (MAD).
Dose Escalation: Cohort B0: GDC-9545 + PalbociclibEXPERIMENTALGDC-9545 will be administered to postmenopausal participants, at a dose lower than the MTD or MAD determined in single-agent dose escalation, in combination with the label-recommended dose of palbociclib.
Dose Expansion: Cohort A1: GDC-9545 Dose 1EXPERIMENTALGDC-9545 will be administered to postmenopausal participants as a single-agent at a dose that is less than or equal to the MTD/MAD (Dose 1).
Dose Expansion: Cohort A2: GDC-9545 Dose 1 + LHRHEXPERIMENTALGDC-9545 will be administered to pre- or perimenopausal participants at a dose that is less than or equal to the MTD/MAD (Dose 1) in combination with an approved LHRH agonist.
Dose Expansion: Cohort A3: GDC-9545 Dose 2EXPERIMENTALGDC-9545 will be administered to postmenopausal participants as a single-agent at a dose that is less than or equal to the MTD/MAD (Dose 2).
Dose Expansion: Cohort A4: GDC-9545 Dose 2 + LHRHEXPERIMENTALGDC-9545 will be administered to pre- or perimenopausal participants at a dose that is less than or equal to the MTD/MAD (Dose 2) in combination with an LHRH agonist.
Dose Expansion: Cohort A5: GDC-9545 Dose 3EXPERIMENTALGDC-9545 will be administered to postmenopausal participants as a single-agent at a dose that is less than or equal to the MTD/MAD (Dose 3).
Dose Expansion: Cohort B1: GDC-9545 + PalbociclibEXPERIMENTALGDC-9545 will be administered to postmenopausal participants, at a dose that is less than or equal to the MTD/MAD, in combination with the label-recommended dose of palbociclib.
Dose Expansion: Cohort B2: GDC-9545 + Palbociclib + LHRHEXPERIMENTALGDC-9545 will be administered to pre- or perimenopausal participants, at a dose that is less than or equal to the MTD/MAD, in combination with the label-recommended dose of palbociclib and an approved LHRH agonist.
Dose Expansion: Cohort C1: GDC-9545 Dose 2 +/- PalbociclibEXPERIMENTALGDC-9545 will be administered to postmenopausal participants at a pre-defined dose level (Dose 2) as a single agent for 14 days, followed by treatment with either GDC-9545 (Dose 2) plus palbociclib or GDC-9545 (Dose 2) alone for the duration of the study, as determined by the investigator.
Dose Expansion: Cohort C2: GDC-9545 Dose 2 + PalbociclibEXPERIMENTALGDC-9545 will be administered to postmenopausal participants at a pre-defined dose level (Dose 2), in combination with the label-recommended dose of palbociclib.
Dose Expansion: Cohort X: GDC-9545 Dose 3EXPERIMENTALGDC-9545 will be administered at a pre-defined dose level (Dose 3) to postmenopausal participants currently receiving clinical benefit with GDC-0927 or GDC-0810 on Studies GO29656 (NCT02316509) or GO29642 (NCT01823835), respectively, upon completion of their studies.

Interventions

NameTypeDescription
GDC-9545DRUGGDC-9545 will be administered orally, once daily, on Days 1-28 of each 28-day cycle, until disease progression, unacceptable toxicity, withdrawal of consent, or study termination.
PalbociclibDRUGPalbociclib will be administered orally, once daily, at the label-recommended dose of 125 mg on Days 1-21 of each 28-day cycle, until disease progression, unacceptable toxicity, withdrawal of consent, or study termination.
LHRH AgonistDRUGThe LHRH agonist (leuprolide acetate, goserelin acetate, or triptorelin pamoate) will be administered by injection once every 4 weeks on Day 1 of each 28-day cycle, according to the label. The investigator will choose the appropriate LHRH agonist approved for use in breast cancer.
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Eligibility Criteria

Age Range18 Years to N/A
SexFEMALE
Healthy VolunteersNo
Study Sites23

Inclusion Criteria for Dose Escalation: * Histologically or cytologically proven diagnosis of adenocarcinoma of the breast with evidence of either locally recurrent disease not amenable to resection or radiation therapy with curative intent or with metastatic disease * Estrogen receptor (ER)-positi...

Countries:United StatesAustraliaSouth KoreaSpainUnited Kingdom
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Competitive Landscape -Breast Cancer 402 trials

Top 20 of 92 competitors

CompanyTickerTrialsLead PhaseDrugs
AstraZeneca PLCAZN47PHASE3Fulvestrant, Capivasertib
Merck & Co., Inc.MRK12PHASE3Pembrolizumab, Paclitaxel, Doxorubicin, Epirubicin, Cyclophosphamide
Eli Lilly and CompanyLLY27PHASE3Abemaciclib, Standard Adjuvant Endocrine Therapy
BioNTech SE Sponsored ADRBNTX7PHASE3DB-1303/BNT323, T-DM1
Gilead Sciences, Inc.GILD13PHASE3Sacituzumab Govitecan-hziy, Eribulin, Capecitabine Product, Gemcitabine, Vinorelbine
Novartis AG Sponsored ADRNVS30PHASE3Ribociclib
Pfizer Inc.PFE34PHASE3ARV-471, Fulvestrant
BeOne Medicines Ltd. Sponsored ADRONC5PHASE3BGB-43395, Letrozole, Abemaciclib, Palbociclib, Ribociclib
Olema Pharmaceuticals, Inc.OLMA5PHASE3Palazestrant, Fulvestrant, Anastrozole, Letrozole, Exemestane
Jazz Pharmaceuticals Public Limited CompanyJAZZ3PHASE3Zanidatamab, Trastuzumab, Eribulin, Vinorelbine, Gemcitabine
Celcuity Inc.CELC3PHASE3Gedatolisib, Palbociclib, Fulvestrant, Alpelisib
Relay Therapeutics, Inc.RLAY2PHASE3Zovegalisib, Capivasertib, Fulvestrant
GSK plc Sponsored ADRGSK2PHASE3Niraparib
Greenwich LifeSciences, Inc.GLSI1PHASE3GLSI-100
Bristol-Myers Squibb CompanyBMY5PHASE2Iza-bren, Nab-paclitaxel, Paclitaxel, Capecitabine, Carboplatin
BriaCell Therapeutics CorpBCTX2PHASE3SV-BR-1-GM, Cyclophosphamide, Interferon infiltration of the inoculation site, Retifanlimab, Treatment of Physician's Choice
Incyte CorporationINCY4PHASE2Ruxolitinib, Capecitabine, Regorafenib
Natera, Inc.NTRA3PHASE2Discontinuation of the anti-HER2 maintenance therapy
Puma Biotechnology, Inc.PBYI3PHASE2Neratinib, Loperamide, Colesevelam
Atossa Therapeutics, Inc.ATOS1PHASE2endoxifen, goserelin
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Recent Changes (Last 90 Days)

LOWAug 14, 2026NCT03332797lastUpdatePostDate: changed
LOWAug 14, 2026NCT03332797lastUpdatePostDate: changed
LOWAug 14, 2026NCT03332797lastUpdatePostDate: changed

Frequently asked questions about GDC-9545

What is GDC-9545 used for?

GDC-9545 is an investigational small molecule being studied for the treatment of locally advanced or metastatic estrogen receptor-positive breast cancer. It is also being evaluated in healthy volunteers for pharmacokinetic studies. The drug is currently in Phase 1 clinical development.

Who makes GDC-9545?

GDC-9545 is being developed by Roche Holding AG, which trades under the ticker RHHBY. The company is conducting clinical trials of the drug in multiple countries, including the United States, Australia, South Korea, Spain, and the United Kingdom.

What phase is GDC-9545 in?

GDC-9545 is in Phase 1 clinical development. It is an investigational drug and has not been approved by regulatory authorities. The ongoing Phase 1 trial is studying the drug alone or in combination with palbociclib and/or luteinizing hormone-releasing hormone agonist in breast cancer patients.

What clinical trials is GDC-9545 in?

GDC-9545 has been studied in three Phase 1 trials. NCT03332797 is an active trial in breast cancer patients, testing the drug alone or with palbociclib and/or LHRH agonist. NCT04274075 and NCT04680273, both completed, evaluated bioavailability and drug metabolism in healthy female volunteers.

Is GDC-9545 being studied in healthy volunteers?

Yes, GDC-9545 has been studied in healthy female volunteers of non-childbearing potential. Two completed Phase 1 trials, NCT04274075 and NCT04680273, evaluated the drug's relative bioavailability, food effect, absorption, metabolism, and excretion in this population.