Pasritamig combination delivers 73% PSA response rate in advanced prostate cancer Phase I study

Johnson & Johnson has reported early Phase I results for a dual-bispecific immunotherapy combination of pasritamig and JNJ-9401 in patients with metastatic castration-resistant prostate cancer.

At the recommended regimen, 73% of patients achieved reductions of at least 50% in prostate-specific antigen levels.

The findings were presented at the Society for Immunotherapy of Cancer 2026 Annual Meeting.

Among 15 patients treated at the recommended regimen, 11 achieved a PSA reduction of at least 50%, while seven, or 47%, achieved reductions of at least 90%.

Four patients reached undetectable PSA levels.

All seven patients who achieved PSA reductions of at least 90% remained on treatment for more than six months without disease progression at the time of the analysis.

The combination uses two bispecific antibodies designed to target different prostate cancer antigens while delivering complementary signals to T cells.

Pasritamig targets kallikrein-related peptidase 2, or KLK2, and is designed to direct T cells toward prostate cancer cells.

JNJ-9401 targets prostate-specific membrane antigen and is intended to provide an additional signal that strengthens and sustains T-cell activity.

Johnson & Johnson described the regimen as the first clinically evaluated dual-tumour-antigen-targeted bispecific antibody combination in prostate cancer.

The ongoing open-label, multicentre Phase I study is assessing safety and preliminary clinical activity in patients with metastatic castration-resistant prostate cancer, also referred to as metastatic androgen pathway modulation-resistant prostate cancer.

As of June 15, 2026, 144 patients had been enrolled in the study.

Patients treated at the recommended regimen had received a median of four previous systemic treatment lines, with a range of two to six.

No Grade 3 or higher treatment-related adverse events were reported among the 15 patients receiving the recommended regimen.

There were also no dose-limiting toxicities or treatment-related adverse events leading to treatment discontinuation or death.

Cytokine release syndrome occurred in three patients, representing 20% of the cohort.

All cases were Grade 1 and presented as temporary fever, with none requiring treatment with tocilizumab.

No cases of immune effector cell-associated neurotoxicity syndrome were reported.

The recommended regimen consists of JNJ-9401 200 mg administered subcutaneously every six weeks together with pasritamig 300 mg intravenously every six weeks, following two initial weekly pasritamig step-up doses.

Johnson & Johnson said the dosing schedule could potentially support treatment in an outpatient setting.

Laura Graham, MD, Assistant Professor of Medicine-Medical Oncology at the University of Colorado School of Medicine, said the depth and duration of the PSA reductions provide encouraging early evidence for the combination in a cancer type where immunotherapy has historically had limited impact.

She added that confirmation in a larger study will be needed to establish the clinical benefit.

The combination has already advanced into the Phase III KLK2-comPAS trial.

The study is evaluating whether adding JNJ-9401 to pasritamig can improve outcomes in patients with metastatic castration-resistant prostate cancer.

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