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Study of patritumab deruxtecan versus drug combination in patients with hormone receptor-positive, HER2-negative advanced or metastatic breast cancer

Fast replyRegistered drugNo placebo
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What is this trial about?

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

This study focuses on treating patients with hormone receptor-positive, HER2-negative breast cancer that has either spread to other parts of the body (metastatic) or cannot be removed by surgery (unresectable locally advanced). The main treatment being tested is patritumab deruxtecan (also known as MK-1022), which will be compared to other standard treatments chosen by doctors, including paclitaxel, capecitabine, doxorubicin, or other similar medications.

The purpose of this research is to determine how well patritumab deruxtecan works compared to standard treatments in controlling the disease and helping patients live longer. The study is designed for patients whose cancer has continued to grow despite previous treatment with hormone therapy and special medications called CDK4/6 inhibitors.

During the study, participants will be randomly assigned to receive either patritumab deruxtecan or one of the standard treatment options. All medications will be given through an intravenous infusion (directly into a vein), except for capecitabine which is taken as tablets by mouth. The treatment will continue as long as it is helping the patient and side effects are manageable.

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 treatment assignment

    You will be randomly assigned to receive either patritumab deruxtecan or another treatment chosen by your physician

    Your physician will select from available treatments including paclitaxel, capecitabine, doxorubicin, or other approved medications

  2. Step 2

    Treatment administration

    If assigned to patritumab deruxtecan: You will receive the medication through intravenous infusion

    If assigned to physician's choice treatment: The medication will be given either through intravenous infusion or as oral medication, depending on the selected treatment

    Your treatment will continue until your disease progresses or you experience unacceptable side effects

  3. Step 3

    Regular monitoring

    Your health status will be regularly evaluated using imaging scans to check if the cancer is responding to treatment

    Your overall physical condition will be assessed using a standard performance scale

    You will complete quality of life questionnaires about your physical functioning, emotional well-being, and pain levels

  4. Step 4

    Safety monitoring

    Your doctor will monitor you for any side effects throughout the treatment period

    Regular health checks will include assessment of any new symptoms or health changes

  5. Step 5

    Study duration

    The study is planned to continue until July 2033

    Your participation will last until your disease progresses or you need to stop treatment for other reasons

Who can join the trial?

8 criteria

  • Must have hormone receptor positive breast cancer that is either locally advanced (cannot be surgically removed) or has spread to other parts of the body (metastatic)
  • Must have confirmation from a central laboratory that the cancer is: - HR-positive (responds to hormone therapy) - HER2-negative (does not have high levels of HER2 protein) - Has evaluable HER3 (another protein) levels from a recent tissue sample
  • Must have had cancer progression or return while on previous treatment with: - CDK4/6 inhibitor (a type of targeted therapy) combined with hormone therapy as first treatment for advanced breast cancer, or - Disease return during or within 24 months after completing treatment with CDK4/6 inhibitor given with hormone therapy after surgery
  • Must be suitable for at least one standard treatment option as determined by the doctor
  • Must have cancer that can be measured using special imaging criteria (RECIST 1.1)
  • If living with HIV, the infection must be well-controlled with anti-HIV medications
  • Must be able to perform daily activities independently or with minimal assistance (ECOG performance status of 0 or 1) within 7 days before joining the study
  • Must be an adult aged 18 years or older

Who cannot join the trial?

14 criteria

  • History of treatment with HER3-targeted therapy (a specific type of cancer treatment targeting HER3 proteins)
  • Active brain metastases (cancer that has spread to the brain) that are not treated and stable
  • Significant heart conditions including:
    • Heart failure (when heart cannot pump blood effectively)
    • Irregular heartbeat that is not controlled by medication
    • Heart attack within the past 6 months
    • Current treatment with other experimental drugs or participation in other clinical trials
    • Severe liver or kidney problems
    • Autoimmune conditions (diseases where the immune system attacks healthy cells) requiring systemic treatment
    • Active infections requiring treatment, including:
      • Hepatitis B
      • Hepatitis C
      • HIV
      • Known allergies to the study medications or their components
      • Pregnancy or breastfeeding
      • Unable to follow study procedures or attend scheduled visits
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Investigated drugs

Patritumab deruxtecan (also known as HER3-DXd) is a targeted therapy medication that works by delivering cancer-fighting substances directly to cancer cells that have high levels of a protein called HER3. It's designed to treat breast cancer cells while minimizing damage to healthy cells. Treatment of Physician's Choice (TPC) refers to a standard treatment option where the doctor selects from available approved therapies based on what they believe will work best for the individual patient. This could include various chemotherapy drugs or other approved treatments for breast cancer.

What is already known about the treatment

Patritumab Deruxtecan – An investigational antibody-drug conjugate administered through intravenous infusion, specifically designed to target HER3-expressing breast cancer cells. This medication is currently being studied in Phase 3 clinical trials for treating hormone receptor-positive, HER2-negative metastatic breast cancer in patients whose disease has become unresectable or locally advanced. The drug works by combining a HER3-targeting antibody with a potent topoisomerase I inhibitor payload, delivering the cytotoxic agent directly to cancer cells that express HER3. It belongs to the class of targeted cancer therapeutics and represents a novel approach in treating hormone receptor-positive breast cancer that has progressed despite previous treatments.

Investigated diseases

Hormone receptor positive breast cancer - A type of breast cancer where cancer cells grow in response to the hormones estrogen and/or progesterone. The cancer cells have special proteins called hormone receptors on their surface that attach to hormones in the bloodstream. When hormones bind to these receptors, they stimulate the cancer cells to grow and divide. This is one of the most common types of breast cancer, typically developing slowly over time. The cancer usually begins in the milk ducts or milk-producing glands of the breast tissue and can spread to other parts of the breast.
Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2025-520582-51-00Protocol codeMK-1022-016Estimated enrolment982 patientsSponsorMerck Sharp & Dohme LLC

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