RARITAN, N.J., February 26, 2026
Johnson & Johnson announced encouraging preliminary results from a Phase 1b clinical study evaluating pasritamig (JNJ-78278343) in combination with docetaxel in patients with metastatic castration-resistant prostate cancer (mCRPC). The data, presented at the 2026 American Society of Clinical Oncology (ASCO) Genitourinary Cancers Symposium, demonstrated deep and durable prostate-specific antigen (PSA) responses, a favorable safety profile, and strong rationale for advancement into Phase 3 trials. The findings position pasritamig as a promising next-generation T-cell engager immunotherapy candidate in advanced prostate cancer.
Promising Efficacy and PSA Response Rates
Pasritamig is a first-in-class bispecific antibody designed to bind CD3 on T cells and human kallikrein 2 (KLK2), a prostate-specific tumor target with minimal expression outside prostate tissue. By redirecting T cells directly to KLK2-expressing cancer cells, pasritamig enables a focused immune attack on prostate tumors while potentially limiting off-target effects. In the Phase 1b study (NCT05818683), 51 patients with mCRPC who had progressed following androgen receptor pathway inhibitor therapy received pasritamig in combination with docetaxel in an outpatient setting. Notably, 45 percent of participants had previously received at least one taxane-based regimen, reflecting a heavily pretreated population with significant unmet need.
The study reported PSA reductions of 50 percent or greater in 64.7 percent of patients overall, and 75 percent among taxane-naïve patients. Even more striking, PSA reductions of 90 percent or greater were observed in 39.2 percent of patients overall and 53.6 percent of taxane-naïve patients. Among taxane-naïve individuals with bone-only metastatic disease, confirmed PSA reductions of at least 50 percent and 90 percent were achieved in 88.2 percent and 76.5 percent of patients, respectively. These data underscore the potential of pasritamig to deliver clinically meaningful antitumor activity in a difficult-to-treat cancer population where survival outcomes remain limited.
Favorable Safety Profile and Outpatient Feasibility
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The combination therapy demonstrated a safety profile consistent with docetaxel alone, with no new or unexpected safety signals identified. The most common treatment-related adverse events included fatigue, alopecia, diarrhea, nausea, peripheral edema, neuropathy, and dysgeusia. Importantly, Grade 3 or higher adverse events attributed to pasritamig occurred in only two percent of patients, compared to 29.4 percent attributed to docetaxel. No cases of cytokine release syndrome or treatment-related deaths were reported. Patients were able to continue pasritamig beyond docetaxel discontinuation, supporting the potential for sustained disease control. The outpatient administration model, combined with the absence of significant immune-related toxicities, strengthens the feasibility of broader clinical adoption should Phase 3 trials confirm efficacy.
Advancement into Phase 3 Development
Based on these encouraging results, Johnson & Johnson is advancing pasritamig into two ongoing Phase 3 studies: KLK2-comPAS (NCT07164443), evaluating pasritamig monotherapy, and KLK2-PASenger (NCT07225946), evaluating the combination with docetaxel. Pasritamig has already received Fast Track designation from the U.S. Food and Drug Administration and Breakthrough Therapy designation in China, reinforcing regulatory confidence in its development pathway. As an investigational T-cell-redirecting immunotherapy, pasritamig represents a differentiated approach aimed at expanding the role of immuno-oncology in prostate cancer, particularly in the metastatic castration-resistant setting where median overall survival remains limited.
Metastatic castration-resistant prostate cancer continues to represent a significant global health burden, with patients often experiencing bone and lymph node metastases and poor long-term outcomes despite available chemotherapy and hormonal therapies. The combination of pasritamig and docetaxel offers a potential new therapeutic strategy designed to enhance immune engagement while maintaining manageable safety.
The preliminary Phase 1b results provide a compelling foundation for Phase 3 evaluation and highlight Johnson & Johnson’s continued investment in innovative oncology drug development. If confirmed in later-stage trials, pasritamig could become an important addition to the treatment landscape for advanced prostate cancer.
Source: Johnson & Johnson press release
