Celldex Therapeutics announced that barzolvolimab, its experimental mast cell-targeting drug, met primary and all secondary endpoints in two pivotal Phase 3 trials for chronic spontaneous urticaria (CSU) — a condition marked by recurring hives and swelling that doesn't respond adequately to standard antihistamines. The combined trials enrolled 1,939 patients and tested two doses of the drug against placebo.

Results showed strong and durable responses: at 12 weeks, both doses significantly outperformed placebo, and the benefit held or improved through week 24. Notably, the drug also worked in patients who had previously failed omalizumab (Xolair), a key existing treatment, and in those with angioedema. Celldex plans to submit a marketing application to the FDA in 2027.

By the Numbers:

• ~42–46% of barzolvolimab patients achieved complete response (no itch or hives) at week 12 vs. ~9–13% on placebo
• ~45–54% complete response rate at week 24 vs. ~15–18% on placebo
• 1,939 patients enrolled across both trials

Why it matters: This is a meaningful win for Celldex, which suffered a setback in July 2026 when barzolvolimab failed in prurigo nodularis trials. The CSU data suggest the drug could offer a new option for patients who don't respond to existing therapies like Xolair, potentially reshaping the treatment landscape for this often-debilitating skin condition.