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A Study of JNJ-78278343 Compared to Placebo for Patients with Advanced Prostate Cancer That No Longer Responds to Hormone Treatment

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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 metastatic castration-resistant prostate cancer, which is a form of prostate cancer that has spread to other parts of the body and no longer responds to treatments that lower testosterone levels. The study will test a medication called JNJ-78278343, which is given as a solution through a needle into a vein. Some people in the study will receive this medication while others will receive placebo. All participants will also continue to receive their usual supportive care during the study.

The purpose of this study is to find out if JNJ-78278343 combined with usual care can help people live longer compared to placebo combined with usual care. The medication works by redirecting certain immune cells in the body to target a specific protein found on prostate cancer cells. People joining this study will have already tried several other treatments for their cancer, including hormone therapies, chemotherapy drugs called taxanes, and possibly other specialized treatments depending on what was available to them and what their doctors recommended.

During the study, participants will receive either the study medication or placebo through an infusion into their vein. They will continue their hormone therapy throughout the treatment period. The study will monitor how long participants live and track their overall health. People in the study should have cancer that has spread to bones or lymph nodes but not to major organs like the liver or lungs. They need to be well enough to carry out daily activities with some limitations but not be completely confined to bed or a chair.

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

    Treatment assignment

    Upon joining the study, you will be randomly assigned to one of two treatment groups. This process is called randomization and ensures fair distribution of participants.

    One group will receive JNJ-78278343 (also called pasritamig), which is a medication that helps immune cells target cancer cells. The other group will receive placebo, which is an inactive substance that looks like the actual medication but contains no active treatment.

    Neither you nor your doctor will know which treatment you are receiving. This is called a double-blind study design.

    Both groups will also receive best supportive care, which includes standard treatments to manage symptoms and maintain quality of life.

  2. Step 2

    Continuation of hormone therapy

    You must continue your ongoing hormone therapy throughout the entire treatment period.

    If you have had surgical removal of the testicles, no additional hormone therapy is needed.

    If you have not had this surgery, you will continue receiving medications that suppress testosterone production. These are called GnRH analogs and may be either agonists or antagonists.

    This hormone therapy must be maintained during all phases of the study treatment.

  3. Step 3

    Study medication administration

    You will receive either JNJ-78278343 or placebo through an infusion into your vein.

    The medication is prepared as a solution for infusion, which means it will be delivered directly into your bloodstream over a period of time.

    The specific dosage, frequency of administration, and duration of each infusion session will be determined by the study protocol and communicated to you by the medical staff.

    The treatment will continue according to the schedule established in the study design.

  4. Step 4

    Regular monitoring and assessments

    Throughout the study, you will undergo regular monitoring to assess how the treatment is affecting you and your condition.

    Blood tests will be performed to check various health indicators, including blood cell counts, kidney function, and liver function.

    Your PSA level (a protein produced by the prostate that can indicate cancer activity) will be measured regularly.

    Your overall health status and ability to perform daily activities will be assessed using the ECOG performance status scale, which ranges from 0 (fully active) to 5.

    Any side effects or changes in your health will be recorded and evaluated.

  5. Step 5

    Ongoing treatment phase

    You will continue receiving the assigned study medication along with best supportive care.

    The treatment will continue as long as it is considered beneficial and you do not experience unacceptable side effects.

    Your medical team will monitor your response to treatment and overall survival, which is the main measure of how well the treatment works.

    The study is expected to continue until May 2029, though your individual participation may be shorter or longer depending on your response to treatment and overall health.

Who can join the trial?

11 criteria

  • You must have prostate cancer that has been confirmed by examining tissue under a microscope, showing a type called adenocarcinoma. Certain other types of prostate cancer are not allowed in this study.
  • Your cancer must have spread to other parts of your body, such as bones or lymph nodes (small bean-shaped organs that are part of your immune system), and the cancer must continue to grow even though you are receiving treatment to lower male hormones.
  • Your PSA level (a protein in your blood that can indicate prostate cancer activity) must be at least 2 nanograms per milliliter at the time of screening.
  • Your doctor must believe that the best next treatment option for you is to join a clinical trial.
  • You must have already received all the standard treatments that could help you live longer and that you were able to receive. These treatments include: at least one type of hormone therapy for prostate cancer and you should not benefit from trying another similar hormone therapy; at least two rounds of chemotherapy using drugs called taxanes, or only one round if a second round is not available or your doctor thinks it would not be safe for you; treatment with a radioactive drug that targets prostate cancer cells, unless this treatment is not available or your doctor thinks it is not right for you; and treatment with a drug called a PARPi if you have a specific genetic change called a BRCA mutation and this treatment is available.
  • You must have had surgery to remove your testicles or be receiving ongoing treatment with medications that lower male hormones, and you must continue this treatment during the study.
  • Your overall health and ability to carry out daily activities must be good enough, rated on a scale where 0 means you are fully active and 2 means you can care for yourself but cannot work.
  • Your kidneys must be working well enough, with a measurement called eGFR (a test that shows how well your kidneys filter waste) of at least 30 milliliters per minute. If you have a blockage in your urinary system, it must be treated before joining the study.
  • Your liver must be working well enough, with certain blood tests showing: ALT and AST (enzymes that indicate liver health) no more than 5 times the upper normal limit, and bilirubin (a substance that shows how well your liver processes waste) no more than 3 times the upper normal limit.
  • Your blood counts must be adequate, including: white blood cells (cells that fight infection) at least 1.0 times 10 to the ninth power per liter; hemoglobin (the part of blood that carries oxygen) at least 8.0 grams per deciliter; and platelets (cells that help blood clot) at least 75 times 10 to the ninth power per liter. You cannot have received blood transfusions or medications to boost blood counts within 28 days before joining the study.
  • You must be male, as this study is only for men.

Who cannot join the trial?

3 criteria

  • Women cannot participate in this study
  • Children and teenagers under 18 years of age cannot participate in this study
  • People who do not have metastatic castration-resistant prostate cancer, which means prostate cancer that has spread to other parts of the body and no longer responds to treatments that lower testosterone levels
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Investigated drugs

Pasritamig is a medication being tested in this clinical trial. It is a type of treatment that helps direct the body's immune system cells (called T-cells) to find and attack prostate cancer cells. Specifically, it works by targeting a protein called human kallikrein 2, which is found on prostate cancer cells. This medication is given along with best supportive care to patients with metastatic castration-resistant prostate cancer, which is an advanced form of prostate cancer that has spread to other parts of the body and no longer responds to hormone treatments that lower testosterone.

What is already known about the treatment

Pasritamig – Pasritamig is an experimental medication currently being studied in phase 3 clinical trials for the treatment of metastatic castration-resistant prostate cancer, which is an advanced form of prostate cancer that no longer responds to hormone therapy and has spread to other parts of the body. This drug is a T-cell-redirecting agent that works by targeting a specific protein called human kallikrein 2, found on prostate cancer cells, and helps the body's immune system recognize and attack these cancer cells. The study is investigating whether pasritamig, when added to best supportive care, can help patients live longer compared to placebo with best supportive care. As a biologic immunotherapy, it represents a novel approach to treating advanced prostate cancer by harnessing the patient's own immune system to fight the disease.

Investigated diseases

Metastatic Castration-resistant Prostate Cancer – This is an advanced form of prostate cancer that has spread beyond the prostate gland to other parts of the body. The disease continues to grow and progress even when the level of testosterone in the body has been reduced to very low amounts through medication or surgery. In this condition, cancer cells have developed the ability to survive and multiply without needing normal levels of male hormones. The cancer may spread to bones, lymph nodes, or other organs throughout the body. Patients with this condition have typically already received treatments to lower testosterone levels, but the cancer has adapted and continues to advance. This represents a later stage in the progression of prostate cancer where the disease has become resistant to standard hormone-based treatments.
Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2025-520927-26-00Protocol code78278343PCR3001Estimated enrolment663 patientsSponsorJanssen Cilag International

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