argenx SE (ARGX) Won Its Phase 3 Myositis Trial. How Much Does the Subgroup Miss Matter?

Argenx SE (NASDAQ:ARGX) achieved a significant victory with the Phase 3 ALKIVIA trial for its VYVGART Hytrulo therapy. The drug demonstrated a 15.4-point mean improvement over placebo in the Total Improvement Score (TIS) at Week 52 for the combined immune-mediated necrotizing myopathy (IMNM) and dermatomyositis population. This result marked the first time a therapy showed statistical significance in treating IMNM.

However, the smaller dermatomyositis subgroup, while showing a numerical 14.5-point advantage, did not reach statistical significance. The IMNM subgroup recorded a 14.8-point treatment difference with a p-value of 0.0048, indicating a strong potential for a market with substantial unmet need. The drug is based on an already commercialized molecule, providing a significant advantage in terms of development and launch risk reduction compared to building a new franchise.

VYVGART generated $1.516 billion in global product net sales in the second quarter, giving argenx SE a commercial platform for this new indication. The trial results appeared by Week 4 and continued through Week 52, even with protocol-directed steroid tapering. The company reported that all six score components favored treatment, with an improvement in skin disease activity as well.

However, the miss in the dermatomyositis subgroup, which has roughly 40,000 U.S. patients, could influence the eventual label, addressable market, physician confidence, or demands for additional evidence. While the miss may reflect the smaller sample size, argenx SE has not released detailed subgroup data to fully judge this question.

The hedge fund database shows 42 funds holding argenx SE at the end of March 2026, a decrease from 48 funds three months earlier. The preliminary conclusion is that ALKIVIA strengthens the VYVGART franchise and creates a credible opportunity in an indication with no approved therapy. However, the dermatomyositis miss leaves an important commercial and regulatory question unresolved, making this a meaningful win but not yet a uniform victory across myositis subtypes.