Celldex CLDX Stock Drops 28% as Phase 3 Barzolvolimab Hives Data Triggers Sell-the-News Reaction Despite Trial Success

Celldex Therapeutics reported positive top-line results Tuesday from its two pivotal Phase 3 EMBARQ-CSU1 and EMBARQ-CSU2 studies of barzolvolimab in adults with chronic spontaneous urticaria, a condition causing persistent hives, yet shares of CLDX fell roughly 28.6% in pre-market trading in a sharp sell-the-news reaction.

Both evaluated dose regimens of barzolvolimab met the primary endpoint, a statistically significant improvement in the weekly urticaria activity score compared to placebo, and cleared all key secondary endpoints as well. Critically, efficacy was sustained or continued deepening through 24 weeks of treatment, consistent with the durable responses the drug had shown in earlier Phase 2 work where complete response rates held out to 76 weeks.

The trials were the largest registration program ever conducted in antihistamine-refractory CSU, enrolling 1,939 patients across more than 500 sites in 43 countries. Results support Celldex's planned Biologics License Application submission to the FDA in 2027. Stifel reiterated its Buy rating on the stock after the data, signaling at least some institutional confidence that the selloff reflected positioning rather than a fundamental change in the drug's prospects.

The steep decline despite clean data reflects a confluence of factors: the stock had gained more than 100% over the prior year as investors priced in a successful readout, and the company had already absorbed a setback in July 2026 when barzolvolimab failed a Phase 2 trial in prurigo nodularis, narrowing the drug's addressable market. The CSU program, now the centerpiece of Celldex's pipeline, will need to carry the approval story through to a BLA filing next year.