argenx efgartigimod hits myositis trial endpoint with 15.4-point TIS gain

argenx's efgartigimod met the Phase 3 ALKIVIA primary endpoint in autoimmune myositis, showing a 15.4-point TIS gain over placebo (p=0.0011).

"These are the first Phase 3 results to show that precision targeting of FcRn with efgartigimod can deliver meaningful benefit in this disease," Luc Truyen, M.D., Ph.D., Chief Medical Officer at argenx, said.

Patients treated with efgartigimod achieved a mean Total Improvement Score (TIS) of 47.95 at Week 52 versus 32.56 for placebo. The Phase 3 portion enrolled 175 patients across immune-mediated necrotizing myopathy (IMNM) and dermatomyositis (DM), with a protocol-mandated corticosteroid taper throughout the 52-week treatment period. Treatment effects were consistent across both subtypes, with clinical improvement observed in muscle and skin measures. The safety profile was consistent with prior efgartigimod studies.

Approximately 100,000 people in the United States live with autoimmune myositis, including about 20,000 with IMNM — a subtype with no approved therapy. Up to 80 percent of patients report long-term disability despite treatment with corticosteroids and broad immunosuppressants. The readout positions efgartigimod for potential label expansion beyond its approved indications in generalized myasthenia gravis and CIDP. Detailed results will be presented at an upcoming medical meeting.

The p-value of 0.0011 means there is a 0.11 percent chance the observed treatment difference occurred by random chance. The Total Improvement Score is a composite measure used in myositis trials that captures muscle strength, physician and patient global assessments, and extramuscular disease activity.

IMNM is the most refractory form of autoimmune myositis, and many patients carry irreversible muscle damage, making meaningful improvement difficult to achieve, according to Rohit Aggarwal, M.D., M.S., Professor of Medicine and Co-Director of the Myositis Center at the University of Pittsburgh, and an ALKIVIA investigator. "In DM, the magnitude of improvement was comparable — and for a community where treatment options remain limited and the burden of chronic steroids is just as heavy, that matters," Aggarwal said.

The ALKIVIA study was a global, randomized, double-blind, placebo-controlled Phase 2/3 trial that enrolled 264 patients total across IMNM, DM, and polymyositis. Participants received weekly subcutaneous injections of efgartigimod PH20 or matched placebo. The trial was conducted across North America, Europe, the Middle East, and Asia-Pacific, including China and Japan, with Zai Lab recruiting Chinese patients under an exclusive license agreement for Greater China.

Efgartigimod is a first-in-class human IgG1 antibody fragment that blocks the neonatal Fc receptor (FcRn), reducing circulating pathogenic IgG autoantibodies while preserving other aspects of immune function. The drug is already approved as VYVGART for generalized myasthenia gravis and as VYVGART Hytrulo for gMG and chronic inflammatory demyelinating polyneuropathy. argenx is also evaluating efgartigimod in Sjögren's disease and systemic sclerosis.

The positive readout gives argenx a potential new market in autoimmune myositis, where current treatment relies on corticosteroids and broad immunosuppressants associated with significant cumulative toxicity. Investors will watch for regulatory filings and the upcoming medical meeting presentation for full efficacy and safety data. argenx hosted a conference call on August 17 at 2:30 PM CET to discuss the results.

This article is for informational purposes only and does not constitute investment advice.