Sanofi SA (SNY) released phase 3 data Friday for amlitelimab, the experimental eczema treatment the company hopes will eventually succeed Dupixent, its blockbuster atopic dermatitis drug. The results tell a story that's becoming familiar in pharma: good news with some asterisks attached.

Amlitelimab is a fully human monoclonal antibody that targets OX40-ligand, taking a different mechanistic approach than Dupixent. The company shared data from two global phase 3 studies involving patients 12 years and older with moderate-to-severe atopic dermatitis, and the drug proved well-tolerated with a safety profile consistent with earlier trials. That's the easy part.

When Combination Therapy Works Better

The SHORE study enrolled 596 patients and tested amlitelimab alongside medium-potency topical corticosteroids. Here, the drug delivered what Sanofi needed: it met all primary and key secondary endpoints compared to placebo.

Significantly more patients receiving amlitelimab every four weeks or every 12 weeks achieved clear or almost clear skin versus placebo participants. The vIGA-AD 0/1 rates hit 28.7% to 32.9% compared to 16.8% for placebo, while EASI-75 improvement reached 46.8% to 50.9% versus roughly 32.3% to 34.2% for placebo with topical steroids.

The studies measured outcomes at week 24, evaluating the proportion of patients reaching at least 75% improvement in the eczema area and severity index (EASI 75) and those achieving validated investigator global assessment scores of 0 (clear) or 1 (almost clear).

The Monotherapy Challenge

Things got messier with COAST 2, which enrolled 547 patients. The study met its primary endpoint at week 24 under US statistical methods, with non-responder imputation rates of 25.3% and 25.7% for amlitelimab monotherapy dosed every four weeks and every 12 weeks, respectively, versus 14.8% for placebo.

But the drug stumbled on co-primary endpoints using European statistical estimands, missing significance for both vIGA-AD 0/1 and EASI-75 compared to placebo. A key secondary endpoint measuring vIGA-AD 0/1 with barely perceptible erythema also failed to reach significance under US estimands.

This isn't amlitelimab's first underwhelming moment. Back in September, the COAST 1 phase 3 study technically met all primary and key secondary endpoints with statistically significant skin clearance, but the results disappointed investors who had hoped for stronger performance.

The Long Game

Sanofi also shared preliminary analysis from the ATLANTIS phase 2 study, showing that amlitelimab dosed every four weeks progressively improved skin clearance and disease severity from week 24 through week 52 in 591 patients. That sustained improvement matters when you're building a case for long-term therapy.

The company is pressing ahead with regulatory plans. Two additional phase 3 studies—AQUA and ESTUARY—are expected to report results in the second half of 2026, with global regulatory submissions planned for the same timeframe. Sanofi clearly believes it has enough evidence to support amlitelimab's potential, even if the data doesn't uniformly sparkle.

Broader Context for Sanofi

The amlitelimab development comes during a bumpy period for Sanofi's pipeline. Earlier this month, the FDA issued a complete response letter rejecting the company's tolebrutinib application for treating non-relapsing secondary progressive multiple sclerosis in adults, citing both efficacy and safety concerns including liver injury risk.

Sanofi shares slipped 0.37% to $46.33 in premarket trading Friday following the amlitelimab data release.