JNJ-78278343

Table of contents

• What is JNJ-78278343?
• How does JNJ-78278343 work?
• Which conditions is it used or studied for?
• How is JNJ-78278343 given?
• What do the clinical trials show?
• Who can take part in these trials?
• What side effects are known?

What is JNJ-78278343?

JNJ-78278343, also known as pasritamig, is an investigational antibody-like drug classified as a protein-based substance.^[1] It has no marketing authorisation in the product records and is supplied by Janssen-Cilag International N.V.^[1] The substance is being developed as a T-cell redirecting agent that targets human kallikrein 2 (KLK2), a protein found at high levels on prostate cancer cells.^[3]

How does JNJ-78278343 work?

Pasritamig is designed to attach to T cells — a type of white blood cell in the immune system — and to KLK2 on cancer cells.^[3] By binding both at once, it redirects the body's own immune cells to recognise and attack the prostate cancer cells that carry KLK2.^[3]

Which conditions is it used or studied for?

• Metastatic castration-resistant prostate cancer (mCRPC) — a form of prostate cancer that has spread to other parts of the body and continues to grow despite hormone-lowering treatment. Both registered trials study pasritamig in this condition.^[1][2]

How is JNJ-78278343 given?

Pasritamig is given as a solution for infusion, administered intravenously (into a vein).^[1][3] The dose reported in the registry records is 0 mg, meaning the specific dose was not disclosed in the register.^[1][2]

What do the clinical trials show?

Two Phase 3 trials of pasritamig in mCRPC are authorised in the EU Clinical Trials Information System.^[1][2] The first (2025-520927-26-00) is a randomised, double-blind, placebo-controlled study of pasritamig plus best supportive care versus placebo plus best supportive care in the late-line setting, enrolling 663 participants and measuring overall survival as its primary outcome.^[1][3] The second (2025-522713-29-00) compares pasritamig combined with docetaxel against docetaxel alone, enrolling 800 participants and measuring radiographic progression-free survival (rPFS) — the time from randomisation until radiographic disease progression per PCWG3 and RECIST v1.1 criteria or death from any cause, whichever occurs first.^[2]

Who can take part in these trials?

Both studies enrol adult participants with metastatic castration-resistant prostate cancer.^[1][2] The first trial focuses on the late-line setting, meaning participants have already received prior treatments.^[3] In this trial, participants are randomly allocated in a two-to-one ratio to receive either pasritamig with best supportive care or placebo with best supportive care.^[3] The second trial includes participants receiving docetaxel, a chemotherapy commonly used in mCRPC, with or without pasritamig.^[2]

What side effects are known?

The supplementary source describes the study design and mechanism of action but does not report specific side effects of pasritamig.^[3] As an investigational substance in ongoing Phase 3 trials, the safety profile is still being evaluated.