BGB-43395 Alone or as Part of Combination Therapies in Participants With Breast Cancer and Other Advanced Solid Tumors

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Status and phase

Phase 1


Hormone-receptor-positive Breast Cancer
Non-small Cell Lung Cancer
Advanced Solid Tumor
Hormone Receptor Positive HER-2 Negative Breast Cancer
Hormone Receptor Positive Malignant Neoplasm of Breast
Metastatic Breast Cancer
HER2-negative Breast Cancer
Hormone Receptor Positive Breast Carcinoma
Advanced Breast Cancer


Drug: BGB-43395
Drug: Fulvestrant
Drug: Letrozole

Study type


Funder types



2023-506888-34-00 (Registry Identifier)

Details and patient eligibility


This is a dose escalation and dose expansion study to compare how well BGB-43395, a cyclin-dependent kinase 4 (CDK4) inhibitor, works as monotherapy or in combination with either fulvestrant or letrozole in participants with hormone receptor positive (HR+) and human epidermal growth factor 2 negative (HER2-) breast cancer (BC) and other advanced solid tumors. The main purpose of this study is to explore the recommended dosing for BGB-43395.


79 estimated patients




18+ years old


No Healthy Volunteers

Inclusion criteria

  • Phase 1a (Dose Escalation) and 1b (Dose Expansion): Participants with histologically or cytologically confirmed advanced, metastatic, or unresectable solid tumors associated with dependency on CDK4, including HR+ breast cancer, ovarian cancer, endometrial cancer, non-small cell lung cancer, and others.
  • Phase 1a: Received prior therapy for their condition (if available) and should be refractory to or intolerant of standard-of-care therapies. In regions where approved and available, participants with HR+ breast cancer must have received at least 2 prior lines of treatment including endocrine therapy and a CDK4/6 inhibitor.
  • Phase 1b: Selected tumor cohorts will include HR+/HER2- breast cancer and additional tumor types.
  • Phase 1b: Participants with HR+/HER2- breast cancer enrolled in regions where CDK4/6 inhibitors are approved and available must have received at least one line of therapy for advanced disease including endocrine therapy and a CDK4/6 inhibitor. Participants can have received up to 2 lines of prior cytotoxic chemotherapy for advanced disease.
  • Stable Eastern Cooperative Oncology Group (ECOG) Performance Status ≤ 1.
  • Female participants with metastatic HR+/HER2- breast cancer must be postmenopausal or receiving ovarian function suppression treatment.
  • Adequate organ function without symptomatic visceral disease.

Exclusion criteria

  • Prior therapy selectively targeting CDK4 (prior CDK4/6 inhibitor therapy is permitted and required in local regions where it is approved and available).
  • Known leptomeningeal disease or uncontrolled, untreated brain metastases.
  • Any malignancy ≤ 3 years before the first dose of study treatment(s) except for the specific cancer under investigation in this study and any locally recurring cancer that has been treated with curative intent (eg, resected basal or squamous cell skin cancer, superficial bladder cancer, or carcinoma in situ of the cervix or breast).
  • Uncontrolled diabetes.
  • Infection requiring systemic antibacterial, antifungal, or antiviral therapy ≤ 28 days before the first dose of study drug(s), or symptomatic COVID-19 infection.
  • History of hepatitis B or active hepatitis C infection.
  • Prior allogeneic stem cell transplantation, or organ transplantation.

Note: Other protocol defined Inclusion/Exclusion criteria may apply.

Trial design

Primary purpose




Interventional model

Sequential Assignment


None (Open label)

79 participants in 2 patient groups

Dose Escalation
Experimental group
Phase 1a: Sequential cohorts of increasing dose levels of BGB-43395 will be evaluated as monotherapy and in combination with either fulvestrant or letrozole to assess for safety and tolerability.
Drug: Letrozole
Drug: Fulvestrant
Drug: BGB-43395
Dose Expansion
Experimental group
Phase 1b: The recommended dose for expansion (RFDE) for BGB-43395 (in combination with fulvestrant or letrozole) from Phase 1a will be evaluated in HR+ breast cancer and selected tumor-specific cohorts.
Drug: Letrozole
Drug: Fulvestrant
Drug: BGB-43395

Trial contacts and locations



Central trial contact

Study Director

Data sourced from

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