Testing BTX-9341 for advanced breast cancer

A First-in-Human, Open-Label, Dose Escalation and Expansion Trial of BTX-9341 in Participants With Advanced and/or Metastatic Breast Cancer

Phase 1 Interventional Biotheryx, Inc. · NCT06515470

This study is testing a new drug called BTX-9341, alone and with another medication, to see if it can help people with advanced hormone receptor positive breast cancer.

Quick facts

PhasePhase 1
Study typeInterventional
Enrollment82 (estimated)
Ages18 Years and up
SexAll
SponsorBiotheryx, Inc. Industry-sponsored
Drugs / interventionschemotherapy
Locations6 sites (Rochester, Minnesota and 5 other locations)
Trial IDNCT06515470 on ClinicalTrials.gov

What this trial studies

This clinical trial evaluates the safety, tolerability, pharmacokinetics, and preliminary efficacy of BTX-9341, both alone and in combination with fulvestrant, in patients with advanced or metastatic hormone receptor positive (HR+)/HER2 negative breast cancer. The study is structured in two parts: a dose escalation phase where participants receive increasing doses of BTX-9341, and a dose expansion phase where the selected dose is administered alongside fulvestrant. Participants will be treated in 28-day cycles, and the study aims to gather important data on how well the drug works and its safety profile.

Who should consider this trial

Good fit: Ideal candidates are individuals with metastatic and/or locally advanced HR+/HER2- breast cancer who have received limited prior chemotherapy and specific lines of endocrine therapy.

Not a fit: Patients with early-stage breast cancer or those who have not received prior endocrine therapy or chemotherapy may not benefit from this study.

Why it matters

Potential benefit: If successful, this treatment could provide a new therapeutic option for patients with advanced breast cancer that is resistant to current therapies.

How similar studies have performed: While this is a first-in-human study, similar approaches in targeting HR+/HER2- breast cancer have shown promise in other trials, indicating potential for success.

Eligibility criteria

Show full inclusion / exclusion criteria
Inclusion Criteria:

* Metastatic and/or locally advanced HR+/HER2- breast cancer (dose escalation: measurable disease and/or at least 1 lytic or mixed \[lytic + sclerotic\] bone lesion that can be assessed by CT or MRI or non-measurable disease \[including bone lesions\]; dose expansion: measurable disease)
* Dose escalation: (a) received not more than 1 chemotherapy in the metastatic/advanced setting; (b) no limit to the lines of endocrine therapy (monotherapy or combination therapy) in the metastatic setting; (c) received CDK4/6 inhibitor therapy
* Dose expansion: (a) received not more than 1 chemotherapy in metastatic/advanced setting; (b) received not more than 2 lines of endocrine therapy (monotherapy or combination therapy) and must have been on prior endocrine therapy for at least 6 months before progression; (c) received at most 2 lines of CDK4/6 inhibitor therapy (1 in the adjuvant setting and 1 in the metastatic setting) and must have been on prior CDK4/6 inhibitor therapy for at least 6 months
* Acceptable hematologic function

  1. ANC ≥ 1500 per mL. Note: Use of growth-factors to maintain the ANC criterion is prohibited.
  2. Platelet count ≥ 100,000 per mL. Note: Use of transfusions or thrombopoietic agents to achieve the baseline platelet count criterion is prohibited.
  3. Hemoglobin ≥ 9.0 g/dL. Note: Packed red blood cell transfusion is allowed up to 14 days prior to trial entry.
* Acceptable liver function

  1. Bilirubin ≤ 2.0 × institutional upper limit of normal (ULN) (or \< 3.0 × institutional ULN if Gilbert's disease is present)
  2. Alanine transaminase (ALT)/aspartate aminotransferase (AST) ≤ 3.0 × institutional ULN (≤ 5.0 × institutional ULN if liver metastases present)
  3. Alkaline phosphatase ≤ 2.5 × institutional ULN (≤ 5.0 × institutional ULN if bone or liver metastases present)
* Able and willing to sign informed consent
* Meets all study requirements in the opinion of the Investigator

Exclusion Criteria:

* RB1 (retinoblastoma) gene mutation
* Symptomatic visceral disease
* Clinical evidence or history of central nervous system metastasis
* Abnormalities in coagulation, such as bleeding diathesis, or treatment with anticoagulants precluding injections of fulvestrant or luteinizing hormone-releasing hormone (LHRH) agonist

Where this trial is running

Rochester, Minnesota and 5 other locations

Study contacts

How to participate

  1. Review the eligibility criteria above with your treating physician.
  2. Visit the official trial page on ClinicalTrials.gov for the most current contact information and recruitment status.
  3. Contact the listed study coordinator or principal investigator to request pre-screening. Pre-screening is free and never obligates you to enroll.
Conditions Breast CancerHR+/HER2-
Last reviewed 2026-06-13 by the Find a Trial editorial team. Information on this page is for educational purposes and is not medical advice. Always consult qualified healthcare professionals about clinical trial participation.