In short
JNJ-78278343 (pasritamig) is an investigational T-cell redirecting antibody-like drug being studied in metastatic castration-resistant prostate cancer (mCRPC). It is a protein-based substance given by intravenous infusion and has no marketing authorisation. Two Phase 3 trials are authorised, enrolling 663 and 800 participants respectively, both testing whether pasritamig improves outcomes compared with placebo or standard treatment.
Key points
- JNJ-78278343 (pasritamig) is an investigational T-cell redirecting agent targeting human kallikrein 2 (KLK2) in prostate cancer cells.
- Both registered trials are Phase 3 studies in metastatic castration-resistant prostate cancer (mCRPC).
- The first trial compares pasritamig plus best supportive care against placebo in 663 participants, measuring overall survival.
- The second trial combines pasritamig with docetaxel chemotherapy in 800 participants, measuring radiographic progression-free survival.
- Both trials are currently authorised but not yet reporting results.
- Pasritamig is given as a solution for infusion into a vein.
What is JNJ-78278343?
JNJ-78278343, also known as pasritamig, is an investigational antibody-like drug classified as a protein-based substance. It has no marketing authorisation in the product records and is supplied by Janssen-Cilag International N.V. 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.
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. By binding both at once, it redirects the body's own immune cells to recognise and attack the prostate cancer cells that carry KLK2.
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.
How is JNJ-78278343 given?
Pasritamig is given as a solution for infusion, administered intravenously (into a vein). The dose reported in the registry records is 0 mg, meaning the specific dose was not disclosed in the register.
What do the clinical trials show?
Two Phase 3 trials of pasritamig in mCRPC are authorised in the EU Clinical Trials Information System. 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. 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.
Who can take part in these trials?
Both studies enrol adult participants with metastatic castration-resistant prostate cancer. The first trial focuses on the late-line setting, meaning participants have already received prior treatments. 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. The second trial includes participants receiving docetaxel, a chemotherapy commonly used in mCRPC, with or without pasritamig.
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. As an investigational substance in ongoing Phase 3 trials, the safety profile is still being evaluated.