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Zanidatamab, tucatinib, capecitabine or eribulin mesylate in HER2-positive advanced breast cancer in adults

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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 studying HER2-positive advanced breast cancer, a type of breast cancer that has spread or cannot be removed with surgery alone. The purpose of the study is to find out whether a treatment plan with zanidatamab, tucatinib, and chemotherapy is safe and may help control the cancer. The chemotherapy used in the study is either capecitabine or eribulin mesylate.

Zanidatamab is given through a vein, while tucatinib and capecitabine are taken by mouth. Eribulin mesylate is also given through a vein. The study begins with a small part where the treatment doses are worked out and checked for safety. After that, more people receive the chosen treatment plan for a longer time. During the study, the cancer and any side effects are watched over time, and treatment may continue as long as it is helping and is tolerated.

Some people may also receive medicines used to help with symptoms or side effects, such as diphenhydramine hydrochloride, loperamide hydrochloride, paracetamol, hydrocortisone sodium succinate, dexamethasone sodium phosphate, and capecitabine or eribulin mesylate depending on the treatment group. A CT scan, which is a type of body image test, may be used during the study to look at the cancer. The study is planned to run from 2026 to 2028.

The research process

The trial runs in 4 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Start of study treatment

    You begin study treatment for her2-positive advanced breast cancer. the study uses a combination of medicines given by mouth and by intravenous administration, which means through a vein.

    The study medicine zanidatamab is given by intravenous administration. the study medicine tucatinib is given by oral tablets. the chemotherapy medicine is either capecitabine, given by mouth, or eribulin mesylate, given by intravenous administration.

    The specific dose, frequency, and duration for these study medicines are not stated in the source data. the study is designed to determine the recommended dose of zanidatamab when it is used with tucatinib and either capecitabine or eribulin.

  2. Step 2

    Background medicines during treatment

    Some additional medicines may be used as background treatment, which means they support the main study treatment.

    The listed background medicines are diphenhydramine hydrochloride, loperamide hydrochloride, paracetamol, hydrocortisone sodium succinate, and dexamethasone sodium phosphate.

    The source data do not give the dose, frequency, or duration for these background medicines.

  3. Step 3

    Assessment of treatment effect and safety

    During the study, the effect of treatment is assessed by checking whether the cancer gets smaller, stays stable, or gets worse.

    For part of the study, the doctor assesses progression-free survival, which means the time from treatment start until the cancer gets worse or death occurs, whichever happens first.

    Other measures include overall response, time to response, duration of response, clinical benefit, and changes in the size of the main tumor spots on scans.

  4. Step 4

    Study period end

    The study runs from the start of treatment until the end of follow-up within the trial period.

    The estimated recruitment start date is 2026-07-01 and the estimated end date is 2028-05-31.

Who can join the trial?

27 criteria

  • Be a male or female adult, meaning 18 years of age or older when signing the consent form.
  • Have HER2-positive advanced breast cancer confirmed by the most recent biopsy, with either HER2 score 3+ or HER2 score 2+ plus confirmation of HER2 amplification by in situ hybridization (ISH), which is a test that looks for extra copies of the HER2 gene.
  • Have unresectable locally advanced or metastatic disease shown on a CT scan or MRI, meaning the cancer cannot be removed with surgery intended to cure it.
  • Have disease that can be measured or evaluated using RECIST v1.1, a standard way to measure how a tumor changes over time.
  • Have had the cancer progress, meaning it got worse, after at least 1 and no more than 3 previous treatments that included anti-HER2 therapy for advanced disease.
  • Be able to understand the study and sign a written informed consent form, which is a document showing that the person agrees to join the study after being informed about it.
  • Be able to provide blood samples at the planned study time points.
  • Have enough bone marrow function, meaning the body can make blood cells well enough, with all of these test results: absolute neutrophil count at least 1.5 × 103/μL, platelets at least 100 × 103/μL, and hemoglobin at least 9 g/dL.
  • Have normal enough blood clotting tests, with INR and aPTT no more than 1.5 times the upper normal limit, unless taking medicine that is known to affect these tests.
  • Have liver test results within the allowed range, with total bilirubin no more than 1.5 times the upper normal limit, or no more than 3.0 times the upper normal limit if the person has Gilbert’s disease and the conjugated bilirubin is no more than 1.5 times the upper normal limit.
  • Have liver enzyme test results within the allowed range, with AST and ALT no more than 3.0 times the upper normal limit, or no more than 5.0 times the upper normal limit if there are liver metastases, meaning cancer that has spread to the liver.
  • Have enough kidney function, with serum creatinine no more than 1.5 times the upper normal limit or creatinine clearance of at least 50 mL/min.
  • For women who can become pregnant, have a negative pregnancy test within 14 days before the first study treatment.
  • For women who can become pregnant and men with a partner who can become pregnant, agree to use two effective birth control methods with a failure rate of less than 1% per year, starting at screening, during the study, and for 12 months after the last study treatment.
  • For women, agree not to donate eggs and not to breastfeed starting at screening, during the study, and for 12 months after the last study treatment.
  • For men, agree not to donate sperm and not to store sperm starting at screening, during the study, and for 12 months after the last study treatment.
  • Be available to attend the treatment visits and follow-up visits.
  • If there are brain metastases, meaning cancer that has spread to the brain, they must meet one of these requirements: the brain metastases are stable for at least 4 weeks after treatment, or they are untreated but do not need immediate local treatment, or they have worsened after local brain treatment but do not need immediate retreatment.
  • If there are untreated brain or central nervous system lesions larger than 2.0 cm on screening brain MRI, the case must be reviewed and approved by the study medical monitor before enrollment.
  • If the person had stereotactic radiosurgery or gamma knife treatment, at least 7 days must have passed before the first study dose.
  • If the person had whole-brain radiotherapy (radiation to the whole brain), at least 24 days must have passed before the first study dose.
  • If the person is taking systemic corticosteroids for brain metastasis symptoms, the total daily dose must be 2 mg or less of dexamethasone or an equal dose of another steroid, unless a lower stable dose is reviewed and approved by the medical monitor.
  • If the person is taking anticonvulsant medicine, meaning medicine used to help prevent seizures, the dose must have been stable for at least 14 days before the first study treatment.
  • Have an ECOG performance status of 0 to 1, meaning they are fully active or only slightly limited in daily activities.
  • Have an expected life expectancy of at least 12 weeks at screening.
  • Provide the most recently available FFPE tumor tissue block, which is a preserved tumor sample stored in wax for testing.
  • For phase II of the study, at least 50% of the participants must have brain metastases.

Who cannot join the trial?

25 criteria

  • Participation in another clinical trial, either interventional (a study that gives a treatment) or observational (a study that only watches what happens), until the study safety visit.
  • Any allergy or hypersensitivity reaction to the study drugs or their ingredients, including a life-threatening allergic reaction to monoclonal antibodies (lab-made proteins used as medicines) or to ingredients in zanidatamab.
  • Ongoing treatment-related toxicity from earlier cancer therapy that has not improved to Grade 1 or less (a mild level) according to standard cancer side effect rules, except for hair loss or other side effects the investigator does not consider a safety risk.
  • Another cancer now, or a cancer within the last 5 years, except for certain very small or early skin and cervical cancers that were fully treated. Some low-risk cancers may still need sponsor review.
  • A major surgery or serious injury within 4 weeks before the first study dose, or a likely need for major surgery during study treatment.
  • Serious heart disease, including an irregular heart rhythm needing treatment, uncontrolled high blood pressure, past or current heart failure (the heart does not pump as well as it should), certain abnormal heart tracing results, conditions that can cause dangerous heart rhythm changes, a heart attack or unstable chest pain within 6 months, or a heart pumping function left ventricular ejection fraction below 50% (the percentage of blood the heart pumps out each beat).
  • Past or current interstitial lung disease or pneumonitis (lung inflammation), especially if steroids were needed, or suspected lung inflammation that cannot be ruled out on scans.
  • Severe breathing problems from another lung illness, such as a recent pulmonary embolism (blood clot in the lung), severe asthma, severe COPD (a long-term lung disease that makes breathing difficult), restrictive lung disease, pleural effusion (extra fluid around the lung), lung scarring after COVID-19, certain autoimmune or inflammatory diseases that affect the lungs, or a past pneumonectomy (removal of one lung).
  • Peripheral neuropathy of Grade 2 or higher, meaning moderate or worse nerve damage that can cause pain, numbness, or tingling.
  • Past serious problems with bleeding, blood clots, intestinal obstruction (blocked bowel), or gastrointestinal perforation (a hole in the stomach or bowel) within 3 months before the study starts.
  • Active infection with hepatitis B or hepatitis C. People with past or resolved hepatitis B may still qualify only if certain blood tests are negative for active infection. People with hepatitis C antibody may qualify only if a test for hepatitis C virus RNA is negative.
  • Recent treatment with any systemic anti-cancer therapy (cancer treatment that works throughout the body), including hormonal therapy, non-CNS radiation (radiation not aimed at the brain or spinal cord), or an experimental drug within 3 weeks before the first study dose.
  • Known HIV infection, unless the infection is well controlled on antiretroviral therapy and all required HIV blood test and treatment stability conditions are met.
  • Any other active infection that is not controlled at the time of enrollment.
  • Known dihydropyridine dehydrogenase (DPD) deficiency, a condition that can make it hard to break down capecitabine.
  • Inability to swallow pills or a major stomach or bowel problem that would prevent the body from properly absorbing oral medicines.
  • Any other serious medical problem or abnormal lab test result that, in the investigator’s judgment, would make study participation unsafe or prevent completion of the study.
  • For the phase II part, any prior treatment with HER2 tyrosine kinase inhibitors or HER2 TKIs (drugs that block HER2 signals inside cancer cells).
  • Prior treatment with both capecitabine and eribulin.
  • Known or suspected leptomeningeal disease (cancer in the thin layers around the brain and spinal cord).
  • Advanced, symptom-causing spread of cancer in the body that could quickly become life-threatening, including very large uncontrolled fluid buildup around the lungs, heart, or abdomen, or pulmonary lymphangitis (cancer spread through lymph vessels in the lungs).
  • A live vaccine within 4 weeks before joining the study.
  • Previous allogeneic bone marrow, stem cell, or solid organ transplantation (receiving tissue or an organ from another person).
  • Not enough time has passed after earlier cancer treatments before randomization: chemotherapy and/or monoclonal antibodies, including ADCs (antibody-drug conjugates), need a washout period of up to 3 weeks; small-molecule targeted therapies need up to 2 weeks or 5 half-lives, whichever is shorter.
  • Need for any medication that is not allowed by the study protocol.
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Investigated drugs

  • zanidatamab

    is an intravenous cancer treatment given through a vein. In this trial, it is being studied as the main new treatment added to standard therapy for people with HER2-positive advanced breast cancer. The goal is to see whether it can help control the cancer better when used with the other study medicines.

  • tucatinib

    is a medicine taken by mouth that targets HER2, a protein found in some breast cancers. In this study, it is combined with zanidatamab and chemotherapy to see if the treatment works better together against the cancer.

  • capecitabine

    is an oral chemotherapy medicine. In this trial, it is one of the chemotherapy options used with zanidatamab and tucatinib. It is given to help slow or stop cancer cell growth.

  • eribulin

    is a chemotherapy medicine given through a vein. In this study, it is another chemotherapy option combined with zanidatamab and tucatinib for some participants with HER2-positive advanced breast cancer.

  • dexamethasone

    is a steroid medicine given by injection or infusion. In this trial, it is used as supportive care, often to help prevent or reduce side effects from treatment, such as allergic reactions or inflammation.

  • hydrocortisone

    is a steroid medicine given by injection or infusion. In this study, it is used as supportive care to help reduce the risk of reaction or discomfort during treatment.

What is already known about the treatment

  • Capecitabine

    Capecitabine is an oral film-coated tablet taken by mouth and swallowed with water, usually as part of cancer treatment. It is a well-established medicine in oncology and is still widely used in medical practice and research, especially for breast and colorectal cancers. It is used to treat different types of cancer, including HER2-positive advanced breast cancer in combination with other medicines, and it works as a “prodrug,” meaning the body changes it into the active drug 5-fluorouracil inside tumor tissue. This active form helps stop cancer cells from making DNA, which slows or stops their growth; it belongs to the class of antimetabolite anticancer medicines.

  • Tucatinib

    Tucatinib is an oral film-coated tablet taken by mouth, usually in combination with other cancer medicines. It is a newer targeted cancer medicine and is well described in current medical literature, with approved use in some countries for HER2-positive breast cancer. It is mainly used to treat HER2-positive advanced breast cancer and works by blocking the HER2 protein inside cancer cells, which helps turn off growth signals that tell the cells to multiply. It belongs to the class of targeted anticancer drugs known as HER2 tyrosine kinase inhibitors.

  • Eribulin mesylate

    Eribulin mesylate is given by intravenous administration as a solution for injection, meaning it is delivered directly into a vein by a healthcare professional. It is an established cancer medicine that remains important in medical practice and research, especially for advanced breast cancer and some other cancers. It is used to treat metastatic or advanced breast cancer when other treatments are not enough, and it works by interfering with the internal “skeleton” of the cancer cell so the cell cannot divide normally. It belongs to the class of microtubule inhibitor anticancer medicines.

  • Zanidatamab

    Zanidatamab is given by intravenous administration, so it is infused into a vein under medical supervision. It is a newer medicine in cancer research and is still being studied in clinical trials, although it has shown promising activity in HER2-positive cancers. It is being investigated for HER2-positive advanced breast cancer, and it works by attaching to the HER2 protein on cancer cells and blocking growth signals while also helping the immune system attack the tumor. It is a targeted monoclonal antibody, which is a type of medicine made to recognize a specific protein on cancer cells.

Investigated diseases

HER2-positive advanced breast cancer - HER2-positive advanced breast cancer is a breast cancer that has spread beyond the breast to other parts of the body and has cells with too much HER2 protein on their surface. It usually grows more quickly than some other breast cancers because the HER2 signal helps the cancer cells multiply and survive. As the disease progresses, tumors may enlarge, spread to nearby tissue, or appear in distant organs such as the bones, liver, lungs, or brain. The disease can also become more widespread over time, with new areas of cancer appearing or existing tumors increasing in size.
Trial detailsLast updated 2 Oct 2026
Age18+ yearsPhasePhase ITrial ID2025-524613-89-00Protocol codeMEDOPP0776Estimated enrolment129 patientsSponsorMedica Scientia Innovation Research S.L.

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