Celldex Falls Despite Positive Phase 3 Chronic-Hives Results

Celldex Therapeutics shares fell sharply—about 13% in early trading, with reports of declines near 15%—despite successful Phase 3 results for barzolvolimab, its experimental treatment for chronic spontaneous urticaria (chronic hives).

Both EMBARQ-CSU1 and EMBARQ-CSU2 met their primary endpoint—improvement in weekly urticaria activity score at week 12—and all key secondary endpoints. In reported data, roughly 42%–46% of treated patients had a complete response at week 12, versus about 9%–13% on placebo; complete-response rates reached 54% by week 24.

The selloff centered on two cases of probable Grade 4 anaphylaxis in a barzolvolimab treatment group. Grade 4 events are life-threatening; one patient was hospitalized and another was treated at a clinic and discharged.

Celldex said the overall incidence was extremely low across roughly 2,400 patients exposed to barzolvolimab and continued to characterize the drug’s 24-week safety profile as favorable. Prior concerns also include neutropenia, which can raise infection risk; reported common effects include hair-color and skin-pigmentation changes.

The studies continue through 52 weeks. Celldex has indicated it plans to submit a U.S. biologics license application in 2027, but longer-term safety follow-up and regulators’ interpretation of the anaphylaxis cases will be important.