argenx (NASDAQ:ARGX) reported positive top-line results from its Phase III ALKIVIA trial of VYVGART Hytrulo in autoimmune myositis, meeting its primary endpoint in a combined population of patients with immune-mediated necrotizing myopathy, or IMNM, and dermatomyositis, or DM.
The study evaluated efgartigimod in a 52-week Phase II/III basket trial that enrolled patients with IMNM, DM and polymyositis. The Phase III portion included 175 patients, all of whom were required to have active muscle weakness at enrollment. The primary analysis ultimately focused on the combined IMNM and DM population.
Primary Endpoint Met in Combined Population
Truyen said the active-treatment arm separated rapidly from placebo and maintained the treatment effect through 52 weeks. The company also reported consistent improvement across the six TIS core measures, including the MMT-8 muscle-strength assessment, as well as benefits in muscle and skin manifestations.
The trial included a mandatory corticosteroid taper beginning at Week 16 and continuing through Week 44, targeting steroid use of 5 milligrams or less. Management said patients maintained treatment benefits during the taper, while several placebo patients required rescue treatment.
IMNM Results Support Planned Submission
In the pre-specified IMNM subgroup, efgartigimod met the primary endpoint with a p-value of 0.0048. At Week 52, mean TIS was 45.05 in the active-treatment group, compared with 30.24 in the placebo group, representing a treatment difference of 14.81 points.
Chief Executive Officer Karen Massey described the results as the first Phase III data set in IMNM. She noted that IMNM can progress quickly and may cause irreversible muscle damage, while no approved therapies currently exist for the condition.
argenx said it has breakthrough therapy designation in IMNM and intends to move rapidly toward a regulatory submission. Massey said the company is preparing for a potential launch in one or both subtypes and expects patient-access efforts following an approval to take several quarters, consistent with prior VYVGART indication launches.
Dermatomyositis Showed Similar Effect Size
In dermatomyositis, the study showed a treatment effect of similar magnitude to that seen in IMNM. Mean TIS at Week 52 was 51.51 for efgartigimod-treated patients, versus 36.96 for placebo, a difference of 14.52 points.
However, the DM subgroup did not reach statistical significance on the primary endpoint. Truyen attributed that outcome to the smaller sample size rather than the observed magnitude of treatment effect. The company also reported an effect on skin disease in DM, including results on the Cutaneous Dermatomyositis Disease Area and Severity Index, or CDASI, though it did not disclose detailed endpoint data during the call.
Management said it will engage the U.S. Food and Drug Administration to determine the regulatory path for DM. Massey said potential options could include seeking a label expansion based on the Phase II and Phase III package or conducting a smaller follow-on study, similar to the company’s approach in seronegative myasthenia gravis.
Safety, Rheumatology Expansion and Pipeline
argenx said the safety and tolerability profile in ALKIVIA was consistent with the established profile of VYVGART Hytrulo and prior trials. Truyen said patients in the study were heavily pre-treated with steroids and immunosuppressants. While there was a slight increase in infections, he said there was no consistent pattern and no change in the company’s view of the treatment’s risk profile.
The company plans to present the complete ALKIVIA data set, including subtype-specific efficacy and safety findings, at a future medical congress.
Massey said the results mark argenx’s first positive Phase III rheumatology data set for VYVGART. The company’s next major rheumatology milestone is a Phase III Sjögren’s syndrome readout expected in the second half of 2027, while a Phase II trial in systemic sclerosis remains ongoing.
Management also said any meaningful increase in selling, general and administrative spending related to a rheumatology launch would be expected in next year’s financial results. The company plans to expand its rheumatology capabilities while leveraging existing neurology-related infrastructure, including patient-support resources.
About argenex (NASDAQ:ARGX)
argenx (NASDAQ: ARGX) is a biotechnology company focused on the discovery, development and commercialization of antibody-based therapeutics for severe autoimmune and neuromuscular diseases. The company uses its proprietary SIMPLE Antibody platform to generate differentiated antibodies and engineered Fc regions, and it pursues mechanisms that modulate the neonatal Fc receptor (FcRn) to reduce pathogenic IgG levels. Argenx’s research and development activities span target identification, preclinical development and late-stage clinical programs aimed at addressing unmet needs in immunology.
The company’s lead product, efgartigimod (marketed as Vyvgart), is an FcRn antagonist developed to reduce circulating IgG antibodies and treat IgG-mediated disorders.
