Johnson & Johnson reports Phase 1b success for pasritamig + docetaxel in mCRPC: 65% PSA50 response, docetaxel-like safety, no CRS. Advances to Phase 3
Written By: Nikita Jha, BPharm
Reviewed By: Pharmacally Editorial Team
Johnson & Johnson shared encouraging preliminary results from a Phase 1b study of pasritamig (JNJ-78278343), a novel bispecific T-cell engaging antibody, combined with docetaxel in patients with metastatic castration-resistant prostate cancer (mCRPC). Presented for the first time at the 2026 ASCO Genitourinary Cancers Symposium, the data show a favorable safety profile matching docetaxel alone, alongside robust prostate-specific antigen (PSA) responses. These findings pave the way for Phase 3 advancement in a disease with limited options.
Pasritamig’s Targeted Immune Approach
Pasritamig stands out as a first-in-class bispecific antibody that binds CD3 on T cells and human kallikrein 2 (KLK2), a prostate-specific protein with minimal expression outside prostate tissue. This design redirects T cells precisely to KLK2-expressing tumor cells, potentially sparing healthy tissue and enabling outpatient administration unlike many T-cell engagers requiring hospital monitoring.
Experts like Professor Shahneen Sandhu from Peter MacCallum Cancer Centre called the results “an important step forward,” noting the combination’s clinical activity in a setting where outcomes remain poor.
Charles Drake, Vice President, Prostate Cancer and Cross Cancer Immuno-Oncology, Johnson & Johnson, highlighted its edge over prior combo failures, with deep PSA declines signaling strong potential.
Key Efficacy Highlights
The open-label study (NCT05818683) enrolled 51 patients with mCRPC post-androgen receptor pathway inhibitor therapy; 45% had prior taxane exposure. As of December 9, 2025, patients had received a median of three prior therapies (range 1-9).
Pasritamig was given IV every six weeks (with step-up dosing in cycle 1), alongside docetaxel every three weeks all in an outpatient setting, using only standard docetaxel premedication.
Notable PSA responses included:
≥50% reductions: 64.7% overall, 75.0% in taxane-naïve patients (88.2% in bone-only disease).
≥90% reductions: 39.2% overall, 53.6% in taxane-naïve (76.5% in bone-only).
Patients continued pasritamig post-docetaxel (median six docetaxel doses, eight pasritamig doses), suggesting durable control.
Safety Aligned with Docetaxel Monotherapy
No new safety signals emerged. Common treatment-related adverse events (≥20%) mirrored docetaxel: fatigue (60.8%), alopecia (41.2%), diarrhea/nausea (31.4% each), peripheral edema (27.5%), neuropathy (25.5%), dysgeusia (23.5%). Pasritamig-specific events (≥10%) were fatigue (33.3%) and non-chronic diarrhea (11.8%). Grade ≥3 events tied to docetaxel in 29.4%; only 2% to pasritamig. Zero cytokine release syndrome or treatment deaths occurred.
Advancing to Phase 3 and Beyond
Two Phase 3 trials are underway: KLK2-comPAS (NCT07164443) tests monotherapy; KLK2-PASenger (NCT07225946) evaluates the docetaxel combo. Pasritamig monotherapy holds Breakthrough Therapy Designation in China and FDA Fast Track status. In mCRPC where median survival spans 13.5-31.6 months amid bone/lymph node spread these data address a critical gap.
This progress underscores Johnson & Johnson’s push for prostate-specific immunotherapies, potentially transforming care for pretreated patients.
Reference
Early study results from Johnson & Johnson show promising antitumor activity with combination of pasritamig and docetaxel in advanced prostate cancer, 26 February 2026, Early study results from Johnson & Johnson show promising antitumor activity with combination of pasritamig and docetaxel in advanced prostate cancer
A Study of JNJ-78278343 in Combination with Either JNJ-63723283 (Cetrelimab), Taxane Chemotherapy, or Androgen Receptor Pathway Inhibitors for Metastatic Prostate Cancer, ClinicalTrials.gov ID NCT05818683, Study Details | NCT05818683 | A Study of JNJ-78278343 in Combination With Either JNJ-63723283 (Cetrelimab), Taxane Chemotherapy, or Androgen Receptor Pathway Inhibitors for Metastatic Prostate Cancer | ClinicalTrials.gov
About Writer
Nikita Jha BPharm
She is a pharmacy graduate with expertise in clinical research, pharmacovigilance, and medical writing. In her words, she is passionate about translating complex scientific data into clear, accurate healthcare communications that advance drug safety and patient care.