ALKIVIA met its primary and key secondary endpoints in the combined IMNM and DM population

First Phase 3 study to demonstrate statistically significant and clinically meaningful benefit in IMNM, an autoimmune myositis subtype with no approved therapies

Consistent, clinically meaningful treatment effect in DM, demonstrating improvements in muscle strength and skin disease activity

Amsterdam, the Netherlands – argenx SE (Euronext & Nasdaq: ARGX), the immunology innovation company, announced that data from the Phase 3 ALKIVIA study demonstrating rapid and sustained improvement with VYVGART^® Hytrulo (efgartigimod alfa and hyaluronidase-qvfc) in patients with autoimmune myositis will be featured in a late-breaking oral presentation (#LB24) at the American College of Rheumatology (ACR) Convergence 2026 on November 11, 2026, from 9:15-9:30 a.m. ET.

Combined IMNM and DM population: Primary and key secondary endpoints met
The study met its primary endpoint in the combined immune-mediated necrotizing myopathy (IMNM) and dermatomyositis (DM) patient population, demonstrating that patients treated with efgartigimod achieved a statistically significant and clinically meaningful 15.4-point greater improvement in mean Total Improvement Score (TIS) at Week 52 versus placebo (p=0.0011; 48.0 vs 32.6). The study also met key secondary endpoints in the combined population, including response rate, time to response, muscle strength, and disease activity.

Efgartigimod was generally well tolerated by patients. The observed safety profile was consistent with prior studies and the known safety profile of efgartigimod.

“These Phase 3 results add to the growing body of evidence that targeting FcRn delivers a meaningful, sustained benefit for people with autoimmune myositis,” said Luc Truyen, M.D., Ph.D., Chief Medical Officer, argenx. “ALKIVIA demonstrates the clinical relevance of reducing pathogenic autoantibodies, strengthening the case for efgartigimod to be the first targeted treatment for IMNM. We are moving with urgency to bring efgartigimod to people living with IMNM, who have no approved treatments, and we remain committed to advancing efgartigimod for people living with DM.”

IMNM: Rapid, sustained improvement supports potential first approved treatment
IMNM patients treated with efgartigimod demonstrated a clinically meaningful 14.8-point greater improvement in mean TIS versus placebo at Week 52 (p=0.0048; 45.1 vs 30.2).

Early, durable response: A greater proportion of patients treated with efgartigimod achieved a mean TIS of 40 or more (TIS ≥ 40) at Week 52 versus those on placebo (22.0 percentage-point difference) and were twice as likely to maintain that response through Week 52.

Greater muscle strength: Patients treated with efgartigimod experienced greater improvement (5.4 points) versus placebo in Manual Muscle Testing-8 (MMT-8), which evaluates strength across eight muscle groups.

Reduced muscle injury: Creatine kinase (CK) levels decreased rapidly in patients treated with efgartigimod and remained lower through Week 52, with a 43.5 percentage-point greater reduction from baseline versus placebo, as well as greater improvement in CK grade (0.9-grade greater reduction). CK is a key biomarker of active muscle injury.

Improvements in disease activity: Patients and physicians both reported greater improvement in disease activity with efgartigimod versus placebo at Week 52 as measured by the Patient Global Assessment of Disease Activity (PGA) and Physician Global Assessment of Disease Activity (MDGA).

Based on the ALKIVIA results, argenx plans to submit a Supplemental Biologics License Application (sBLA) with the U.S. Food and Drug Administration (FDA) for efgartigimod in IMNM by the end of 2026, supported by a Breakthrough Therapy Designation from the FDA.

DM: Clinically meaningful treatment effect supports targeting FcRn
In the DM patient population, a clinically meaningful 14.5-point greater improvement versus placebo in mean TIS at Week 52 was observed (p=0.1093; 51.5 vs 37.0), though statistical significance was not reached in this smaller cohort.

Early, sustained response: A greater proportion of patients treated with efgartigimod achieved TIS ≥ 40 versus placebo (27.2 percentage-point difference). Separation from placebo patients was evident from Week 4 and maintained through Week 52.

Improved skin disease: Patients treated with efgartigimod showed a clear improvement in skin disease severity (5.6-point greater improvement at Week 52) versus placebo, as measured by the Cutaneous Dermatomyositis Disease Area and Severity Index (CDASI), with improvement seen from Week 4.

Improved disease activity: Patients and physicians both reported greater improvement in disease activity with efgartigimod versus placebo at Week 52, as measured by the PGA and MDGA.