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Study on the Safety and Effects of Zanidatamab, Palbociclib, and Fulvestrant for Patients with Advanced or Metastatic HER2-Positive, HR-Positive Breast Cancer

Verified siteRegistered drugNo placebo
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What is this trial about?

A plain-language summary of the goals, design and what participants do

This clinical trial is focused on studying a type of breast cancer known as HER2-positive, HR-positive breast cancer. This type of cancer is characterized by the presence of certain proteins and hormone receptors that can promote the growth of cancer cells. The study involves a combination of treatments to evaluate their safety and how well they are tolerated by patients. The treatments being studied include a new medication called JZP598, which contains the active substance zanidatamab, and two other medications, palbociclib and fulvestrant. These medications are used together to see if they can effectively manage the disease.

The purpose of the study is to find a suitable dose of JZP598 when used with palbociclib and fulvestrant and to assess the combination's ability to control the cancer. The study is divided into two parts. In the first part, researchers will determine the best dose of JZP598 to use with the other medications. In the second part, they will evaluate how well this combination works in treating the cancer. Participants will receive the medications through different methods: JZP598 is given as an infusion, palbociclib is taken orally as a capsule, and fulvestrant is administered as an injection.

Throughout the study, participants will be monitored for any side effects and how their cancer responds to the treatment. The study aims to provide valuable information on the effectiveness and safety of using these medications together for treating HER2-positive, HR-positive breast cancer. The trial is expected to continue until early 2026, with the goal of improving treatment options for patients with this type of breast cancer.

The research process

The trial runs in 5 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Initial assessment

    Upon joining the study, an initial assessment is conducted to confirm eligibility. This includes a review of medical history and current health status.

    A new or archived tumor sample is required for central review to confirm HER2-positive and HR-positive status.

  2. Step 2

    Treatment initiation

    The treatment phase begins with the administration of zanidatamab (JZP598) via intravenous infusion. The dosage is determined based on the initial assessment.

    Alongside zanidatamab, fulvestrant (Faslodex 250 mg) is administered through intramuscular injection.

    Additionally, palbociclib (IBRANCE 125 mg) is taken orally in the form of hard capsules.

  3. Step 3

    Ongoing treatment

    The treatment continues with regular administration of the medications. Zanidatamab is given intravenously, fulvestrant intramuscularly, and palbociclib orally.

    The frequency and dosage of each medication are adjusted based on individual response and tolerance.

  4. Step 4

    Monitoring and evaluation

    Regular monitoring is conducted to evaluate the safety and effectiveness of the treatment. This includes checking for any side effects or adverse reactions.

    Blood tests and imaging studies may be performed to assess the response to treatment and adjust the regimen as necessary.

  5. Step 5

    Completion of treatment

    The treatment phase concludes as per the study protocol or if the patient experiences significant improvement or adverse effects.

    A final assessment is conducted to evaluate the overall response to the treatment and to plan any necessary follow-up care.

Who can join the trial?

15 criteria

  • Must have a confirmed diagnosis of breast cancer that is either locally advanced (cannot be removed by surgery) or has spread to other parts of the body. The cancer must be **HER2-positive** and **HR-positive**. **HER2-positive** means the cancer has high levels of a protein called HER2, and **HR-positive** means the cancer grows in response to hormones like estrogen or progesterone.
  • Must be able to provide a new or recent tumor sample for testing to confirm HER2 status.
  • Must have received previous treatments with specific cancer drugs: trastuzumab, pertuzumab, and ado-trastuzumab emtansine (T-DM1). If these treatments were not received due to lack of access or medical reasons, eligibility may still be possible after discussion with the study team.
  • Must have areas of cancer that can be measured or evaluated according to specific criteria.
  • Must be 18 years of age or older.
  • Must have a good general health status, as measured by a score of 0 or 1 on a specific scale used by doctors.
  • Must have a life expectancy of at least 3 months, as judged by the study doctor.
  • Must have certain levels of blood cells and liver and kidney function within specific ranges, as determined by blood tests.
  • Must have a healthy heart function, as shown by a test called **LVEF** (left ventricular ejection fraction).
  • Any side effects from previous cancer treatments must have improved to a mild level, except for hair loss or mild nerve damage.
  • If female and able to have children, must have a negative pregnancy test before starting the study.
  • If able to have children, must agree to use two reliable methods of birth control during the study and for 12 months after the last dose of study medication.
  • Female participants must agree not to breastfeed or donate eggs during the study and for 12 months after the last dose of study medication.
  • Male participants must agree not to donate sperm during the study and for 12 months after the last dose of study medication.
  • Must sign a consent form agreeing to participate in the study and understand what it involves.

Who cannot join the trial?

6 criteria

  • Patients who do not have **breast cancer** that is **locally advanced** (meaning it has spread to nearby areas but not to distant parts of the body) or **metastatic** (meaning it has spread to distant parts of the body).
  • Patients whose breast cancer is not **HER2-positive**. HER2 is a protein that can promote the growth of cancer cells. In some cancers, high levels of HER2 are present.
  • Patients whose breast cancer is not **HR-positive**. HR stands for hormone receptor, and HR-positive means the cancer cells grow in response to hormones like estrogen or progesterone.
  • Patients who are not within the specified age range for the study.
  • Patients who are not part of the specified clinical trial groups.
  • Patients who are considered part of a vulnerable population, which may include individuals who are unable to give informed consent or are at higher risk of harm.
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Investigated drugs

  • ZW25

    is an investigational medication being studied for its potential to treat certain types of breast cancer. It is being tested in combination with other medications to determine the best dose and to evaluate its safety and effectiveness in patients with advanced or metastatic breast cancer that is positive for HER2 and hormone receptors.

  • Palbociclib

    is a medication used to treat certain types of breast cancer. It works by inhibiting proteins that are involved in cell division, which can help slow down or stop the growth of cancer cells. In this trial, it is being used in combination with other treatments to assess its effectiveness in patients with advanced breast cancer.

  • Fulvestrant

    is a medication used to treat hormone receptor-positive breast cancer. It works by blocking the effects of estrogen in the body, which can help slow the growth of cancer cells that rely on this hormone. In this study, it is being combined with other medications to evaluate its role in treating advanced breast cancer.

What is already known about the treatment

  • ZW25

    This medication is administered intravenously and is currently being studied in clinical trials for its effectiveness in treating breast cancer, specifically in patients with locally advanced or metastatic HER2-positive, HR-positive breast cancer. ZW25 is a promising treatment option, as it targets the HER2 protein on cancer cells, potentially inhibiting their growth. It is classified as a monoclonal antibody, which means it is designed to bind to specific proteins on cancer cells, helping the immune system to attack them.

  • Palbociclib

    This medication is taken orally in the form of capsules and is already approved for use in treating certain types of breast cancer. It is being studied in combination with other drugs to enhance its effectiveness. Palbociclib works by inhibiting specific proteins called cyclin-dependent kinases, which are involved in cell division, thereby slowing down the growth of cancer cells. It is classified as a CDK4/6 inhibitor.

  • Fulvestrant

    This medication is administered via intramuscular injection and is used in the treatment of hormone receptor-positive breast cancer. It is being evaluated in combination with other therapies to improve outcomes for patients. Fulvestrant works by binding to estrogen receptors on cancer cells, blocking the effects of estrogen and leading to the degradation of these receptors. It is classified as an estrogen receptor antagonist.

Investigated diseases

Breast Cancer – Breast cancer is a disease where cells in the breast grow uncontrollably. It can begin in different parts of the breast, most commonly in the ducts or lobules. The disease can be classified based on the presence of certain receptors, such as hormone receptors (HR) and human epidermal growth factor receptor 2 (HER2). In cases where the cancer is HER2-positive and HR-positive, it means the cancer cells have more HER2 proteins and hormone receptors than normal cells. This type of breast cancer can be locally advanced, meaning it has spread to nearby tissues, or metastatic, meaning it has spread to other parts of the body. The progression of the disease can vary, with some cases growing slowly and others more rapidly.
Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IITrial ID2023-508135-30-00Protocol codeZWI-ZW25-202Estimated enrolment121 patientsSponsorJazz Pharmaceuticals Ireland Limited

sourced from the EU Clinical Trials Register and site verification

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