The study met its primary endpoint in the combined population of patients with immune-mediated necrotizing myopathy (IMNM) and dermatomyositis (DM). At 52 weeks, the treatment delivered an average improvement in the Total Improvement Score (TIS) that was 15.4 points higher than placebo, with scores of 47.95 and 32.56, respectively.

The treatment effect appeared as early as week four and was sustained throughout the study, including during the gradual tapering of corticosteroids.

The results are particularly encouraging in IMNM, where the study also met its primary endpoint in the prespecified subgroup analysis, with a 14.8-point advantage versus placebo. According to argenx, this is the first phase 3 study to demonstrate a statistically significant and clinically meaningful improvement in this disease, for which no treatment is currently approved.

In dermatomyositis, the improvement observed was of a similar magnitude, at 14.5 points, but did not reach the threshold for statistical significance, with argenx pointing to the smaller size of this cohort.

These data could open up a new indication for argenx's Vyvgart franchise and reinforce its strategy of expanding efgartigimod across multiple autoimmune diseases

KBC Securities' view

In a note, analysts say the company plans to file an accelerated approval application for IMNM and will discuss a potential filing for DM with US health authorities. The Belgian investment bank said it was disappointed that dermatomyositis (DM) did not reach statistical significance, even if argenx believes the magnitude and consistency of the data provide a solid basis for regulatory discussions and a potential filing.

As for immune-mediated necrotizing myopathy (IMNM), it believes the opportunity amounts to several billion dollars.

KBC Securities' rating remains Buy with a target price of €890, implying upside potential of 21.9%.