Argenx was recently dubbed a high-risk, high-reward "moonshot" biotech stock, offering investors tremendous upside if clinical trials panned out. On Thursday, investors saw the flip side of that scenario.

Shares of the Amsterdam-based drugmaker sank 14% to $795.50, pacing toward their worst session since December 2023, after Argenx unexpectedly scrapped a late-stage clinical trial evaluating Vyvgart in patients with Sjögren's disease.

The decision followed a recommendation from an independent data monitoring committee that determined the trial was likely to miss its primary endpoint, Argenx said. Researchers had been evaluating Vyvgart in patients with moderate-to-severe Sjögren's disease, a chronic autoimmune disorder characterized by dry eyes, fatigue, and joint pain.

Vyvgart is Argenx's biggest revenue driver. A blockbuster drug, it topped $1 billion in sales during its first full year on the market. Building on that momentum, the company has sought to expand its target market by pursuing new indications and exploring alternative delivery methods.

The decision to discontinue the trial points to very little efficacy, "if any," rather than a simple "near miss," UBS analysts noted Thursday. UBS had modeled peak annual sales for Vyvgart in Sjögren's disease at $3.5 billion. In 2025, the broader franchise generated $4.2 billion globally.

RBC Capital Markets analyst Luca Issi described the setback as "clearly unfortunate." However, he asserted that while the trial's cancellation removes what he viewed as the stock's most compelling catalyst for 2027, the market's selloff is "way overdone."

Sjögren's disease varies widely in how it presents, progresses, and responds to treatment, making patient selection for trials particularly challenging, Bernstein analysts pointed out. Although Novartis reported positive results with its own candidate last year, broad progress in the field remains slow, with no major therapeutic breakthroughs in over two decades before then, the analysts added.

Vyvgart is currently approved as an intravenous infusion for generalized myasthenia gravis in nearly a dozen markets, including the U.S., Japan, and the European Union. It is also approved in Japan for the treatment of immune thrombocytopenia.

A subcutaneous formulation, branded as Vyvgart Hytrulo, is approved in the U.S., China, and several other countries. Additionally, a pre-filled syringe for self-injection received U.S. approval in April 2025 for two autoimmune conditions.

Separately, argenx announced Thursday that it plans to advance a celiac disease asset -- acquired earlier this year through its $2.2 billion purchase of Forte Biosciences -- into late-stage clinical development.