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Evaluation of zongertinib, fulvestrant and goserelin acetate in patients with HR‑positive HER2‑negative advanced breast cancer

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What is this trial about?

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

The study focuses on hormone receptor‑positive/HER2‑negative advanced breast cancer that carries HER2 mutations. This type of breast cancer grows in response to hormones, does not have excess HER2 protein, and has a genetic change in the HER2 gene that may affect how the disease behaves. Participants will receive a combination of three medicines: an injection of fulvestrant, a daily oral tablet of zongertinib, and an implanted dose of goserelin acetate. The aim of the trial is to determine how many patients experience tumor shrinkage, measured as the objective response rate, which reflects the proportion of people whose tumors become smaller or disappear.

During the trial, patients will start treatment and then return for regular visits where doctors will check for side effects and perform imaging scans, such as CT or MRI, to see how the tumors are changing. The scans are evaluated using a standard set of rules called RECIST, which helps doctors decide whether the cancer is responding, staying the same, or getting worse. Treatment continues as long as it is tolerated and the disease does not progress, with follow‑up visits scheduled at set intervals to monitor health and tumor size.

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

    Study enrollment and baseline procedures

    After joining the study you will sign the informed consent form and complete initial health assessments required by the investigators.

  2. Step 2

    Goserelin acetate implantation

    A goserelin acetate implant delivering 3.6 mg is placed under the skin as directed by the study protocol. the implant releases medication over a period defined by the protocol.

  3. Step 3

    Fulvestrant injection

    You will receive a fulvestrant injection of 500 mg administered by a healthcare professional. the route is intramuscular injection as specified in the study.

  4. Step 4

    Zongertinib oral therapy

    You will start taking a zongertinib oral tablet containing 120 mg as directed by the study protocol. the tablet is film‑coated and should be swallowed with water.

  5. Step 5

    Continuation of treatment through both stages

    The study consists of two stages. during both stages you will continue to receive the goserelin acetate implant, the fulvestrant injection, and the zongertinib tablet according to the trial schedule until the end of the study or until discontinuation criteria are met.

Who can join the trial?

17 criteria

  • You must be able to understand why the study is being done and sign a written consent form.
  • You cannot have had more than two previous chemotherapy treatments for your advanced cancer (an ADC counts as one treatment line).
  • You must not have received any drug that blocks HER2 using a tyrosine kinase inhibitor; other HER2‑targeted medicines and fulvestrant are allowed.
  • Your blood, liver, and kidney tests must be within safe ranges (for example, white blood cells above 3.0 × 10⁹/L, platelets above 100 × 10⁹/L, liver enzymes not too high, and kidney function measured by eGFR ≥ 30 mL/min/1.73 m²).
  • Any side effects from earlier cancer treatments must have healed to a mild level (grade ≤ 1) except for hair loss or other low‑risk problems.
  • If you have a stored tumor sample (a formalin‑fixed paraffin‑embedded block), you should be willing to give it for analysis, though it is not required.
  • Women who could become pregnant must have a negative pregnancy test and use a highly effective birth‑control method from screening until two years after the last study dose; they also cannot donate eggs, breast‑feed, or donate breast milk during this time.
  • Men who could father a child must be surgically sterile or use an acceptable contraception method from screening until two years after the last study dose; they also cannot donate or bank sperm during this period.
  • You need to have a life expectancy of at least 12 weeks at the time of screening.
  • You must be 18 years of age or older when you sign the consent form.
  • Women who are pre‑ or perimenopausal and men must be receiving a hormone‑blocking drug called an LHRH analogue for at least 28 days, or have confirmed post‑menopausal hormone levels; post‑menopausal women are also eligible.
  • You must have a confirmed diagnosis of breast adenocarcinoma that cannot be removed surgically and has spread (unresectable locally advanced or metastatic) as shown on a CT scan or MRI.
  • Your tumor must be hormone‑receptor positive (estrogen‑receptor or progesterone‑receptor present in at least 1 % of cells) and HER2‑negative (tested as 0‑1+ by immunohistochemistry or 2+ with a negative in‑situ hybridization test).
  • You must have a known activating HER2 mutation that has been confirmed by the Guardant360® circulating tumor DNA test.
  • Your disease must be measurable according to the RECIST v1.1 criteria (a standard way doctors measure tumor size).
  • Your overall health status must be ECOG 0‑1 (fully active or able to carry out light work).
  • You must have disease progression after at least one line of hormonal therapy, which includes a CDK4/6 inhibitor; if you received a CDK4/6 inhibitor as adjuvant (post‑surgery) treatment, progression must have occurred after at least 12 months of that therapy and within 12 months after finishing it.

Who cannot join the trial?

23 criteria

  • Already taking part in another clinical trial, whether it is testing a new treatment or just observing, until the safety visit of this study.
  • Having serious heart or blood‑vessel problems, such as painful inflammation of the heart lining (pericarditis), unstable chest pain (unstable angina), a heart attack (myocardial infarction), heart bypass surgery, moderate to severe heart failure (New York Heart Association Class II‑IV), or a stroke or mini‑stroke (cerebrovascular accident or transient ischemic attack) within the past 6 months.
  • Having uncontrolled irregular heart rhythm (atrial fibrillation) or other heart rhythm problems of grade 2 or higher, a prolonged heart‑beat interval on an ECG (QTc >470 ms for women or >450 ms for men), a known tendency for a long QT interval (including family history of long QT syndrome or sudden death before age 40), or taking medicines that lengthen the QT interval.
  • Having a left‑ventricle pumping ability (left ventricular ejection fraction) below 50% as measured by a heart scan (MUGA) or ultrasound (ECHO).
  • Having a current or past non‑infectious lung scarring condition (interstitial lung disease) or lung inflammation (pneumonitis) that needed steroids, or a suspected lung problem that cannot be ruled out by imaging.
  • Having a bleeding disorder (coagulopathy) or a recent history (within 6 months) of deep‑vein clot (deep vein thrombosis) or lung clot (pulmonary embolism), unless the clot was treated and stable for at least 28 days.
  • Having chronic hepatitis B virus infection that is active and not yet treated with suppressive antiviral medication, or hepatitis C infection that is currently being treated or still shows virus in the blood.
  • Having HIV infection with a low immune cell count (CD4+ count < 350 cells/µL), a high amount of virus in the blood (viral load > 400 copies/µL), not being on antiretroviral therapy, or having started therapy less than 4 weeks ago, or having had an AIDS‑related serious infection in the past year.
  • Having any other active infection that is not under control at the time of enrollment.
  • Having severe liver disease (Child‑Pugh class C or a score of 10‑15).
  • Having uncontrolled seizures, serious brain disorders, or a significant psychiatric condition that could affect safety or the ability to follow the study plan.
  • Having a known problem with substance abuse or any other serious uncontrolled medical condition that the doctor believes makes participation unsafe.
  • Being pregnant, breastfeeding, or not willing to use highly effective birth control as required by the study.
  • Having received any approved or experimental cancer treatment within 21 days (or five drug half‑lives, whichever is shorter) before starting the study drugs, except for fulvestrant which may be given sooner.
  • Having any serious medical problem or abnormal lab test result that the investigator thinks would make participation unsafe or prevent completing the study.
  • Being unable or unwilling to follow the study requirements, as judged by the investigator.
  • Needing to continue taking medicines that could interfere with the safety or conduct of the trial.
  • Having active, uncontrolled, or symptomatic cancer spread to the brain or spinal fluid (known as CNS metastases or leptomeningeal disease), as shown by symptoms, swelling, or growth.
  • Having another cancer (or a cancer diagnosed within the past 5 years) except for certain low‑risk cancers such as cervical carcinoma in place, non‑melanoma skin cancer, or early‑stage uterine cancer that have been treated with cure intent.
  • Being allergic or having a hypersensitivity reaction to the study drugs (zongertinib or fulvestrant) or any of their ingredients.
  • Having a condition that prevents normal absorption of oral medication, such as ongoing gut blockage, severe diarrhea, Crohn’s disease, ulcerative colitis, previous gastric bypass surgery, or an inability or unwillingness to swallow pills.
  • Having received radiation therapy within 2 weeks before the first dose of the study drugs, except for palliative radiation to areas other than the chest, which is allowed up to 1 week before the first dose.
  • Having had major surgery or a serious injury within 14 days before the first dose of the study drugs, or expecting to need major surgery during the study period.
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Investigated drugs

  • FULVESTRANT

    is an injectable medication that works by blocking the estrogen receptors on breast cancer cells. By preventing estrogen from attaching to these receptors, it helps slow the growth of tumors that need estrogen to grow. In this study, fulvestrant is given together with another drug to see how well the combination works against advanced breast cancer.

  • GOSERELIN

    is an implantable hormone therapy that reduces the body’s production of estrogen. It is placed under the skin and slowly releases medication over time, lowering estrogen levels that can fuel certain breast cancers. In this trial, goserelin is used as a background treatment to keep estrogen low while the main study drugs are tested.

  • BI 1810631

    is an oral medication that targets specific changes (mutations) in the HER2 gene found in some breast cancers. By blocking the activity of the mutated HER2 protein, it aims to stop cancer cells from growing and spreading. In this study, BI 1810631 is being tested in combination with fulvestrant to see if the two drugs together improve the response in patients with advanced hormone‑receptor‑positive, HER2‑negative breast cancer that carries HER2 mutations.

What is already known about the treatment

  • Fulvestrant

    Fulvestrant is given as an intramuscular injection, typically a 500 mg dose administered monthly. It is an approved drug that has been widely studied and used for advanced hormone‑receptor‑positive breast cancer. The medicine works by binding to estrogen receptors and causing them to be broken down, which stops estrogen‑driven tumor growth. It belongs to the class of selective estrogen receptor degraders, a type of hormonal therapy.

  • Goserelin acetate

    Goserelin acetate is supplied as a small implant that is placed under the skin, releasing a 3.6 mg dose over about a month. It is an approved gonadotropin‑releasing hormone (GnRH) agonist that is used in several hormone‑sensitive cancers, including breast cancer. The implant suppresses the pituitary gland, lowering the production of hormones that can feed tumor growth. It is classified as a GnRH agonist hormone‑therapy.

  • Zongertinib

    Zongertinib is taken as an oral film‑coated tablet, usually 120 mg once daily. It is still an investigational drug and has not yet received regulatory approval, being studied in early‑phase trials for HER2‑mutated breast cancer. The tablet blocks the activity of the HER2 protein’s kinase domain, preventing signals that make cancer cells grow and divide. It is categorized as a HER2‑targeted kinase inhibitor, a form of targeted cancer therapy.

Investigated diseases

Hormone receptor‑positive, HER2‑negative advanced breast cancer - Hormone receptor‑positive, HER2‑negative advanced breast cancer is a form of breast cancer that grows in response to estrogen or progesterone and does not overexpress the HER2 protein. The term “advanced” indicates that the cancer has spread beyond the breast or cannot be removed surgically. As the disease progresses, cancer cells can infiltrate nearby lymph nodes and travel through the bloodstream to distant organs such as bone, liver, lungs, or brain. Tumor growth may be gradual, but over time the lesions can increase in size and number, leading to worsening symptoms. The cancer can become less responsive to hormone signals, making further spread more likely.
Trial detailsLast updated 2 Oct 2026
Age18+ yearsPhasePhase IITrial ID2026-525328-10-00Protocol codeMEDOPP0958Estimated enrolment25 patientsSponsorMedica Scientia Innovation Research S.L.

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