Johnson & Johnson disclosed that its Phase 1b study of pasritamig, a T‑cell engager targeting human kallikrein 2 (KLK2), achieved encouraging efficacy in 51 patients with metastatic castration‑resistant prostate cancer (mCRPC). The combination of pasritamig with docetaxel produced a 50 % or greater decline in prostate‑specific antigen (PSA) in 64.7 % of all patients and 75.0 % of taxane‑naïve patients; 90 % or greater PSA reductions were seen in 39.2 % of the overall cohort and 53.6 % of taxane‑naïve patients. In the bone‑only disease subgroup, 88.2 % of patients achieved a 50 % or greater PSA decline and 76.5 % reached a 90 % or greater reduction.
The safety profile of the pasritamig/docetaxel regimen mirrored that of docetaxel alone. The most common treatment‑related adverse events were fatigue (60.8 %), alopecia (41.2 %), diarrhea and nausea (each 31.4 %). Grade 3 or higher events attributable to docetaxel occurred in 29.4 % of patients, while pasritamig contributed only 2 %. Importantly, no cytokine‑release syndrome or treatment‑related deaths were reported, addressing a key safety concern for T‑cell‑engaging therapies.
These findings support the continuation of pasritamig into two Phase 3 trials—KLK2‑comPAS (monotherapy) and KLK2‑PASenger (combination with docetaxel). The drug has already earned Breakthrough Therapy Designation in China and Fast‑Track status from the U.S. FDA, positioning it for accelerated regulatory review if the Phase 3 data confirm the Phase 1b results. The study reinforces Johnson & Johnson’s multi‑pronged prostate‑cancer strategy, which also includes a KLK2‑directed radioligand and a KLK2 CAR‑T candidate, and follows the company’s recent acquisition of Halda Therapeutics for its RIPTAC platform.
From a business perspective, the positive Phase 1b data strengthen Johnson & Johnson’s oncology pipeline and could expand its market share in the mCRPC space, where median overall survival remains limited. The results also validate the company’s investment in KLK2 as a highly specific target, potentially offering a therapeutic advantage over other prostate‑cancer modalities that target antigens expressed in non‑tumor tissues.
Professor Shahneen Sandhu, an investigator in the study, noted, “These data represent an important step forward for patients with advanced prostate cancer. 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.”
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