Johnson & Johnson reported preliminary Phase 1b results for its investigational bispecific antibody pasritamig in combination with docetaxel in patients with metastatic castration-resistant prostate cancer, showing encouraging efficacy alongside a safety profile consistent with docetaxel alone.

Pasritamig monotherapy received Breakthrough Therapy Designation in China as well as Fast Track designation from FDA.

The data, presented for the first time at the 2026 American Society of Clinical Oncology (ASCO) Genitourinary Cancers Symposium, showed no new or unexpected safety signals and clinically meaningful prostate-specific antigen (PSA) responses, supporting advancement into Phase III studies.¹

Pasritamig (JNJ-78278343) is a first-in-class bispecific T-cell engaging antibody designed to bind CD3 on T cells and human kallikrein 2 (KLK2), a prostate cancer target with minimal expression outside prostate tissue.²

By activating and directing T cells to KLK2-expressing tumor cells, the therapy is intended to focus immune activity on prostate cancer cells and support administration in a doctor’s office setting.

“These data represent an important step forward for patients with advanced prostate cancer,” said Professor Shahneen Sandhu, associate professor, consultant medical oncologist and researcher at Peter MacCallum Cancer Centre, and study investigator. “In a disease where outcomes remain poor for many patients, seeing encouraging clinical activity alongside a favorable safety profile in combination with docetaxel reinforces the potential of this approach and supports further clinical development.”

Johnson & Johnson currently has two ongoing Phase III studies evaluating pasritamig in metastatic castration-resistant prostate cancer: KLK2-comPAS (NCT07164443) as monotherapy and KLK2-PASenger (NCT07225946) in combination with docetaxel.

Trial Design

In the study, 51 patients with metastatic castration-resistant prostate cancer whose disease had progressed following androgen receptor pathway inhibitor therapy received pasritamig plus docetaxel as of Dec. 9, 2025. Approximately 45% had received at least one prior taxane-based regimen.²

Reductions of 50% or greater in PSA levels were achieved in 64.7% of patients overall and in 75.0% of taxane-naïve patients. Reductions of 90% or greater were observed in 39.2% of patients overall and 53.6% of taxane-naïve patients. Among taxane-naïve patients with bone-only disease, confirmed PSA reductions of at least 50% and 90% were observed in 88.2% and 76.5% of patients, respectively.²

Patients received a median of six docetaxel doses every three weeks and eight pasritamig doses every six weeks and were able to continue pasritamig beyond docetaxel discontinuation.²

What were the adverse events?

The most common treatment-related adverse events occurring in at least 20% of patients included fatigue, alopecia, diarrhea, nausea, peripheral edema, peripheral sensory neuropathy and dysgeusia.

Grade 3 or higher treatment-related adverse events attributed to docetaxel were observed in 29.4% of patients, compared with 2% attributed to pasritamig. No patients experienced cytokine release syndrome of any grade or treatment-related deaths.²

“Based on these findings, we are increasingly confident in the potential of pasritamig to meaningfully improve outcomes for people with prostate cancer,” said Charles Drake, Vice President, Prostate Cancer and Cross Cancer Immuno-Oncology, Johnson & Johnson. “The ability to combine pasritamig with docetaxel, where prior approaches in the field have fallen short, gives us a strong foundation for Phase 3 development.”

References

1. Early study results from Johnson & Johnson show promising antitumor activity with combination of pasritamig and docetaxel in advanced prostate cancer Johnson &Johnson February 26, 2026 https://www.prnewswire.com/news-releases/early-study-results-from-johnson--johnson-show-promising-antitumor-activity-with-combination-of-pasritamig-and-docetaxel-in-advanced-prostate-cancer-302698631.html
2. A Study of JNJ-78278343 in Combination With Either JNJ-63723283 (Cetrelimab), Taxane Chemotherapy, or Androgen Receptor Pathway Inhibitors for Metastatic Prostate Cancer National Library of Medicine February 13, 2026 https://clinicaltrials.gov/study/NCT05818683