argenx SE shares opened 8.9% higher on August 17 after the company reported positive Phase 3 ALKIVIA results for VYVGART Hytrulo in adults with autoimmune myositis, the first late-stage success for a targeted therapy in a disease area still dominated by corticosteroids and broad immunosuppression. The stock opened at $927.33 versus a prior close of $851.29, lifting the Nasdaq-listed company's market capitalization to about $61.25 billion. In the combined immune-mediated necrotizing myopathy, or IMNM, and dermatomyositis, or DM, population, efgartigimod achieved a statistically significant 15.4-point greater improvement in mean Total Improvement Score at Week 52 versus placebo, 47.95 versus 32.56, with a p-value of 0.0011. Benefits appeared by Week 4 and were sustained through a year of treatment during protocol-mandated corticosteroid tapering. In prespecified subtype analyses, IMNM met the primary endpoint with a 14.8-point greater improvement and a p-value of 0.0048, while DM showed a clinically meaningful 14.5-point improvement but did not reach statistical significance in the smaller cohort, with a p-value of 0.1093. argenx said all six core set measures favored efgartigimod, including muscle strength, physical function and broader disease activity, with skin disease improvement also observed in DM. The safety profile was consistent with prior studies. The Phase 3 portion enrolled 175 patients, and argenx's Greater China partner Zai Lab recruited Chinese patients into the global trial under their 2021 agreement.