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A Study of BNT323 and BNT327 for Patients with Advanced Breast Cancer to Test Safety and Effectiveness

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What is this trial about?

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

This study is looking at advanced breast cancer and metastatic breast cancer, which are types of breast cancer that have spread beyond the original tumor or to other parts of the body. The study will test two investigational treatments called BNT323 and BNT327, which will be given through an infusion into a vein. These treatments will be tested both alone and in combination with each other. Some patients in the study will receive only BNT323, some will receive only BNT327, and some will receive both treatments together. The study focuses on patients whose breast cancer has a specific status related to a protein called human epidermal growth factor receptor 2 or HER2, which is measured in tumor samples.

The purpose of the study is to find the best dose of BNT323 when used together with BNT327, to check if these treatments are safe, and to see if they help patients with advanced breast cancer. The study is divided into two parts. In the first part, different doses of BNT323 combined with BNT327 will be tested to find the recommended dose for further testing. In the second part, the effectiveness and safety of BNT323 alone, BNT327 alone, and the combination of both treatments will be compared to see how well they work in shrinking or controlling the cancer.

During the study, patients will receive the assigned treatment and will be monitored for any side effects and for how their cancer responds to the treatment. The study will measure things like whether the tumors shrink or disappear, how long any response to treatment lasts, and whether the disease remains stable. Patients will need to have tumors that can be measured and will undergo heart function tests before starting treatment to ensure their heart is working properly. The study will track various safety measures including any unwanted effects from the treatments, whether treatment doses need to be changed or stopped, and overall how well patients tolerate the medications.

The research process

The trial runs in 7 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Treatment assignment

    Upon joining the study, you will be assigned to one of two parts based on the study design.

    In Part I, the focus is on finding the right dose of BNT323 when combined with BNT327. This is called dose escalation.

    In Part II, you may receive BNT323 alone, BNT327 alone, or both medications together. This is called dose optimization.

    The assignment depends on which cohort and treatment arm you are placed in.

  2. Step 2

    Pre-treatment assessment

    Before starting treatment, your heart function will be checked. This is done using either an echocardiography (a type of ultrasound of the heart) or a MUGA scan (a test that shows how well your heart pumps blood).

    Your left ventricular ejection fraction, which measures how well your heart pumps blood, must be 55% or higher.

    A recent tumor sample will be tested to confirm the HER2 status of your cancer. HER2 is a protein that can affect how breast cancer grows.

    Your disease will be measured according to standard criteria called RECIST 1.1 to confirm that you have measurable tumors.

  3. Step 3

    Treatment administration

    You will receive the study medication through an intravenous infusion, which means the medication is delivered directly into a vein.

    BNT327 is provided as a powder that will be mixed into a liquid solution before being given to you through infusion.

    BNT323 is also provided as a powder that will be mixed into a liquid solution before being given to you through infusion.

    The treatment is given in cycles. Each Cycle 1 is monitored closely to check for any dose-limiting side effects.

    The exact dosage and frequency will depend on which part of the study you are in and which dose level or treatment arm you are assigned to.

  4. Step 4

    Monitoring during treatment

    Throughout the study, you will be monitored for any side effects or adverse events.

    Special attention will be given to serious side effects, side effects that are grade 3 or higher (more severe), and side effects that may be related to the study medication.

    If you experience certain side effects, your treatment may be paused, the dose may be reduced, or treatment may be stopped.

    Your response to treatment will be assessed regularly to see if the tumors are shrinking, staying the same, or growing.

  5. Step 5

    Response evaluation

    Your tumors will be evaluated to determine your response to treatment.

    A complete response means all signs of cancer have disappeared.

    A partial response means the tumors have shrunk significantly.

    Stable disease means the tumors have neither grown significantly nor shrunk significantly.

    The time it takes for you to respond to treatment, how long the response lasts, and whether the disease is controlled will all be measured.

    In certain cohorts, the time until the disease progresses or other outcomes will also be tracked.

  6. Step 6

    Continuation of treatment

    Treatment will continue in cycles as long as you are benefiting from it and not experiencing unacceptable side effects.

    The study team will regularly assess whether it is safe and appropriate for you to continue receiving the medication.

  7. Step 7

    End of treatment and follow-up

    Once you stop receiving the study medication, you will continue to be followed to monitor your health and disease status.

    Information about your overall survival and disease progression may continue to be collected even after treatment ends.

Who can join the trial?

7 criteria

  • You must have breast cancer that has been confirmed by laboratory tests, which is either locally advanced (cancer that has grown into nearby tissues), cannot be removed by surgery, or has metastasized (spread to other parts of the body)
  • Your cancer must have a confirmed HER2 status, which is a protein found on some breast cancer cells that is tested by a laboratory using a recent tumor sample
  • Your cancer must have a documented history of HER2 expression, meaning the amount of HER2 protein present must match specific group definitions for this study
  • You must have measurable disease, which means your cancer can be seen and measured on scans according to specific medical guidelines
  • Your heart must be functioning well, with a left ventricular ejection fraction (a measure of how well your heart pumps blood) of 55% or higher, as measured by a heart scan within 28 days before joining the study
  • You must be an adult, as the study accepts participants who are 18 years of age or older
  • Both men and women can participate in this study

Who cannot join the trial?

3 criteria

  • The source data does not provide specific exclusion criteria for this clinical trial
  • Exclusion criteria are reasons why someone cannot join a study, such as having certain other medical conditions, taking specific medications, or having particular test results that would make participation unsafe or affect the study results
  • If you are interested in this trial, the research team will review all requirements with you during the screening process, which is when doctors check if you meet all conditions to participate
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Investigated drugs

  • BNT323

    is an investigational medication being tested in this trial for the treatment of advanced breast cancer. It is being studied both alone and in combination with another medication to see how well it works and how safe it is for patients.

  • BNT327

    is an investigational medication being tested in this trial for the treatment of advanced breast cancer. It is being studied both alone and in combination with another medication to see how well it works and how safe it is for patients.

What is already known about the treatment

  • BNT323

    BNT323 is an investigational medication currently being studied in clinical trials for the treatment of advanced and metastatic breast cancer. It is being tested both as a single therapy and in combination with another experimental drug called BNT327 to determine the most effective and safe dosing approach. The medication is administered as part of a research study to evaluate how well it works in shrinking tumors and its safety profile in patients whose breast cancer has spread or progressed. At the molecular level, the specific mechanism of how BNT323 works is still under investigation as part of ongoing clinical research.

  • BNT327

    BNT327 is an experimental medication being evaluated in clinical trials for patients with advanced and metastatic breast cancer. This drug is being tested alone and in combination with BNT323 to find the best treatment approach and determine appropriate dosing levels. It is given to patients as part of a controlled research study aimed at understanding its effectiveness in producing tumor responses and monitoring any side effects that may occur. The exact way BNT327 works at the cellular and molecular level is part of the ongoing clinical investigation to better understand its therapeutic potential.

Investigated diseases

  • Advanced Breast Cancer

    Advanced breast cancer refers to breast cancer that has grown beyond the early stages within the breast tissue and nearby lymph nodes. The disease involves cancer cells that have spread more extensively in the breast area or to regional lymph nodes but may not yet have reached distant organs. As the condition progresses, the tumor continues to grow and may affect surrounding tissues. Symptoms can include a noticeable lump, changes in breast shape or size, skin changes, and nipple discharge. The cancer cells multiply and invade nearby structures, making the disease more complex to manage. This stage represents a progression from earlier, more localized forms of breast cancer.

  • Metastatic Breast Cancer

    Metastatic breast cancer is an advanced stage of breast cancer where cancer cells have spread from the breast to distant parts of the body. Common sites of spread include bones, lungs, liver, and brain. The disease occurs when cancer cells break away from the original tumor and travel through the bloodstream or lymphatic system to other organs. Once established in distant sites, these cancer cells form new tumors that continue to grow. Symptoms vary depending on where the cancer has spread and may include bone pain, shortness of breath, persistent fatigue, and unexplained weight loss. This represents the most advanced stage of breast cancer progression.

Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase ITrial ID2024-517979-20-00Protocol codeBNT323-03Estimated enrolment383 patientsSponsorBioNTech SE

sourced from the EU Clinical Trials Register and site verification

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