argenx: Phase 3 ALKIVIA shows efgartigimod delivers rapid, sustained benefit in autoimmune myositis

Study topline

The Phase 3 ALKIVIA study met its primary endpoint in the combined immune‑mediated necrotizing myopathy (IMNM) and dermatomyositis (DM) population, with a 15.4‑point greater mean Total Improvement Score (TIS) at Week 52 for efgartigimod versus placebo (48.0 vs 32.6; p=0.0011). Key secondary endpoints, including response rate, time to response, muscle strength and disease activity, were also met. Efgartigimod was generally well tolerated and safety was consistent with prior studies.

IMNM results

In IMNM patients, efgartigimod produced a clinically meaningful 14.8‑point greater mean TIS at Week 52 (45.1 vs 30.2; p=0.0048). A 22.0 percentage‑point higher proportion achieved TIS ≥40 and responders were twice as likely to sustain response through Week 52. Muscle strength (MMT‑8) improved by 5.4 points versus placebo, creatine kinase (CK) levels fell rapidly and remained lower with a 43.5 percentage‑point greater reduction, and both patient and physician global assessments favored efgartigimod.

Dermatomyositis results

DM patients showed a 14.5‑point greater mean TIS (51.5 vs 37.0) that did not reach statistical significance (p=0.1093) in the smaller cohort. Clinical signals included a 27.2 percentage‑point higher TIS ≥40 rate, early separation from placebo from Week 4 maintained to Week 52, and a 5.6‑point greater improvement in skin severity (CDASI), alongside improved PGA and MDGA scores.

Trial design and next steps

ALKIVIA was a global, randomized, double‑blind, placebo‑controlled, operationally seamless Phase 2/3 study that randomized 265 patients with active disease on background therapy; 175 patients received treatment in the Phase 3 portion with a protocol‑mandated corticosteroid taper. argenx plans to submit a supplemental BLA to the FDA for efgartigimod in IMNM by the end of 2026, supported by a Breakthrough Therapy Designation.