Janux Therapeutics' JANX007 Data Update: Mixed Results and Market Reaction

Janux Therapeutics has released new data for its investigational T-cell engager JANX007, currently in phase 1a/1b trials for advanced castration-resistant prostate cancer. The update, while showing promise, has led to a significant drop in the company's stock price.

Clinical Trial Results and Market Impact

As of October 15, 109 patients were treated across dose-escalation and expansion studies. In the latest data cut, 8 out of 27 eligible patients (30%) demonstrated confirmed and unconfirmed partial responses. This marks a decrease from the previously reported 50% response rate, where 4 out of 8 RECIST-eligible patients showed partial responses.

The prostate-specific antigen (PSA) response rates remain impressive, with 12 out of 14 patients (86%) receiving the selected phase 1b dosing regimen achieving a 50% or greater reduction in PSA levels from baseline. Additionally, 7 out of 13 patients (54%) saw a 90% or more reduction.

Despite these promising results, Janux's stock plummeted by 48% following the data release, falling from $33.99 to $17.7 per share.

Comparative Analysis and Expert Opinions

Analysts from Evercore and William Blair remain optimistic about JANX007's potential, despite the market's negative reaction. Jonathan Miller of Evercore noted that the findings compare "very favorably" to Novartis' Pluvicto and other investigational T-cell engagers, although they failed to match Janux's own previous results.

William Blair analysts acknowledged the "fair criticism" regarding the lowered RECIST response rate but deemed the stock drop an "overreaction." They cited favorable cytokine release syndrome (CRS) mitigation strategies and different dosing regimens as factors supporting JANX007's continued development.

Safety Profile and Future Outlook

Janux's updated CRS mitigation efforts have resulted in a strong safety profile. One undisclosed protocol led to zero grade 3 CRS cases, with most cases being grade 1. This improvement could potentially allow for outpatient administration of the therapy.

The overall progression-free survival (PFS) was reported at 7.3 months across 108 patients receiving at least 2 mg of JANX007. In the 6-mg or 9-mg cohorts, which will be studied further, 29 patients demonstrated a median PFS of 7.9 months. These results are competitive with other bispecific T-cell engagers in development, such as Amgen's xaluritamig and Johnson & Johnson's pasritamig.

While specific timelines have not been disclosed, analysts anticipate the next update from the phase 1b trial to come in 2026, potentially reestablishing investor confidence in the program.