Argenx has posted positive Phase 3 results for its blockbuster antibody drug Vyvgart in myositis, a group of inflammatory muscle diseases — a win that could open a new market for one of biotech’s biggest recent successes.
In the ALKIVIA study, Vyvgart Hytrulo (efgartigimod, given as a subcutaneous injection) delivered a 15.4-point greater mean improvement than placebo on the Total Improvement Score — a measure of muscle strength and physical function — after 52 weeks. The company described a “rapid and sustained benefit” starting around week four and lasting a year while patients tapered off steroids. Shares rose more than 13% on the news.
Which patients
The trial covered forms of myositis including immune-mediated necrotising myopathy (IMNM) — an aggressive disease that breaks down muscle cells, affecting roughly 20,000 patients with no approved treatments — and dermatomyositis (DM). The effect was strong in the IMNM group; in dermatomyositis the improvement was meaningful but not statistically significant.
Why it matters
Vyvgart is already approved for generalized myasthenia gravis and has expanded into chronic inflammatory demyelinating polyneuropathy, generating about $2.9 billion in revenue in the first half of 2026. “For people living with myositis, the goal is straightforward: regain strength and function, and get off long-term steroids,” said University of Pittsburgh myositis researcher Rohit Aggarwal. Analysts called the data a meaningful expansion opportunity for the roughly $60-billion company.