Argenx shares jump after positive Phase 3 results in autoimmune myositis trial

Argenx's stock surged by over 7% in early Monday trading following the announcement that its drug efgartigimod achieved the primary objective in a late-stage trial for treating adults with autoimmune myositis. The Phase 3 study revealed substantial and enduring advantages compared to a placebo across two types of the muscle-weakening condition, including one with no current approved treatments.

Efgartigimod-treated patients exhibited a 15.4-point greater improvement in mean total improvement score at 52 weeks than those on placebo, marking the first Phase 3 trial to demonstrate significant enhancements in the rare immune-mediated necrotizing myopathy subtype, which currently lacks approved therapies. While patients with dermatomyositis, another subtype, showed comparable clinical improvements, the smaller group did not reach statistical significance, according to the company.

Argenx emphasized that the drug demonstrated a favorable safety profile, aligning with previous trials. For years, individuals with autoimmune myositis have primarily relied on corticosteroids and broad immunosuppression, with those suffering from immune-mediated necrotizing myopathy (IMNM) having no approved treatment options. These are the first Phase 3 results to illustrate that precision targeting of FcRn with efgartigimod can yield meaningful benefits in this disease, stated Luc Truyen, Argenx's chief medical officer.