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Closed (no longer recruiting)Last updated: 5 February 2024

ACE-Breast03: This Phase II trial is trying to understand the effectiveness of a new targeted therapy (ARX788) in people with HER2-positive metastatic breast cancer who have not responded to other targeted therapies (T-DM1, T-DXd, Tucatinib)A Global, Phase 2 Study of ARX788 in HER2-positive, Metastatic Breast Cancer Patients Whose Disease is Resistant or Refractory to T-DM-1 or T-DXd, and/or Tucatinib-containing Regimens

Clinical summary


This is a Phase II, open-label trial with one experimental arm, designed to assess the anti-cancer activity and safety of ARX788 in HER2+ metastatic breast cancer patients whose disease is resistant or refractory to T-DM1, and/or T-DXd, and/or tucatinib-containing regimens. Participants will receive ARX788 every 4 weeks (Q4W) by intravenous infusion.


This trial is treating patients with HER2+ metastatic breast cancer.


Breast Cancers Breast





Trial Acronym


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Trial Identifiers

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Trial sponsor

Ambrx, Inc.

Scientific Title

A Global, Phase 2 Study of ARX788 in HER2-positive, Metastatic Breast Cancer Patients Whose Disease is Resistant or Refractory to T-DM-1 or T-DXd, and/or Tucatinib-containing Regimens



  • Age ≥ 18 years and older
  • Life expectancy ≥ 6 months
  • Unresectable or metastatic breast cancer subjects
  • Presence of at least one measurable lesion per RECIST v 1.1
  • Subjects must have an adequate tumor sample available for confirmation of HER2 status
  • Subjects must have had prior treatment with no more than 5 prior regimens of systemic treatment in the metastatic setting. One of these prior treatments must have been treatment with T-DXd.
  • Subjects with stable brain metastases
  • Acute toxicities from any prior therapy, surgery, or radiotherapy must have resolved to Grade ≤1 as per the NCI-CTCAE v 5.0, except alopecia
  • Adequate organ functions
  • Willing and able to understand and sign an informed consent inform and to comply with all aspects of the protocol


Any subject who meets any of the following criteria is excluded from the study:

  • History of allergic reactions to any component of ARX788.
  • Prior history of interstitial lung disease, pneumonitis, or other clinically significant lung disease
  • Any active ocular infections or chronic corneal disorders
  • History of congestive heart failure, unstable angina pectoris, unstable atrial fibrillation, or cardiac arrhythmia within 12 months prior to enrollment
  • Grade 3 to 4 peripheral neuropathy (NCI CTCAE v 5.0). Patients with Grade 2 neuropathy can be enrolled at investigator's discretion
  • History of unstable central nervous system (CNS) metastases
  • Current severe, uncontrolled systemic disease (eg, clinically significant cardiovascular, pulmonary, or metabolic diseases)
  • Any uncontrollable intercurrent illness, infection (including subjects with active, symptomatic Covid-19 infections), or other conditions that could limit study compliance or interfere with assessments
  • Exposure to any other investigational or commercial anticancer agents or therapies administered with the intention to treat malignancy within 14 days before the first dose of ARX788


  • You have had treatment but your cancer has gotten worse or has not responded to the treatment you have been given.
  • You have had treatment, but your cancer has come back.
  • Your cancer has spread to other parts of the body.


  • You have certain types of non-cancer medical conditions.
  • You have had certain treatments, surgical procedures or drugs.

Clinical trials have complex eligibility criteria.

Ask your doctor if this trial could be right for you.

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