Star drug suffers heavy blow! Argenx (ARGX.US) terminates thyroid eye disease drug trial, stock price hits seven-month largest drop.

Belgian biotechnology company Argenx (SE: ARGX.US) has announced that it will terminate late-stage trials of an experimental drug for autoimmune diseases affecting the eyes, causing its stock price to plummet the most in seven months. Argenx stated that based on the recommendation of an independent data monitoring committee, the drug Efgartigimod (branded as Vyvgart) being evaluated in adult patients with moderate to severe thyroid eye disease will be discontinued. The company's stock price fell as much as 9.7% on the Brussels stock market, marking the biggest drop since May 8. As of writing, the stock has dropped 5.31% in pre-market trading. The termination of this trial has disrupted the company's goal to treat 50,000 patients by 2030. Argenx expects to announce results next year for four other late-stage clinical trial projects targeting various autoimmune diseases, three of which involve Vyvgart. Analyst Michael Shah noted in a report that the termination of the thyroid eye disease trial "came as a surprise and directly implies the exclusion of a potential U.S. patient market of approximately 100,000 individuals". He added that this adds an "additional burden to successful key data readouts in 2026" in areas such as severe myasthenia gravis, dermatomyositis, and primary immune thrombocytopenia. Argenx stated that the independent data monitoring committee conducted an futility assessment of unblinded data from patients who completed 24 weeks of treatment in the late-stage study. The company plans to present the data at future medical conferences. According to a statement on Monday, the drug showed good safety and tolerability characteristics, with no new safety signals identified. Since its listing on the Brussels stock market in July 2014, Argenx's stock price has surged over 8000%, with the fate of the company closely tied to its only approved drug Vyvgart. This blockbuster drug is currently approved for the treatment of generalized myasthenia gravis and chronic inflammatory demyelinating polyneuropathy, and has been approved in Japan for the treatment of primary immune thrombocytopenia. Other analysts remain optimistic about Argenx's long-term prospects. Analyst Sebastiaan VanderScott from Van Lanschot Kempen wrote in a report, "While thyroid eye disease could have added $800 million to our current peak sales estimate of $11 billion, this is only a small part of our valuation of Vyvgart. We see the emotional oversell as an opportunity to buy one of Europe's must-hold biotech stocks."