(Bloomberg) -- Argenx SE shares plunged after the Dutch biotech said preliminary results from a study suggest its only medicine failed in a trial for a rare bleeding disorder. 

Fewer volunteers taking the drug, Vyvgart, had improved blood clotting than those taking a placebo in a study, the company said Tuesday. The patients suffered from primary immune thrombocytopenia, in which insufficient platelets lead to bleeding, bruising and fatigue. 

The stock fell as much as 17% in early trading, dropping to the lowest level in four months. 

The setback comes as Argenx tests Vyvgart, the first of a new class of medicines that prevent a common antibody from being recycled back into the blood, for more than a dozen rare conditions. 

“This is not the outcome we had hoped for patients, but setbacks are part of pioneering a new class of medicines,” said Luc Truyen, the company’s chief medical officer.

The results announced Tuesday appear to conflict with another study testing the drug for primary immune thrombocytopenia, which showed it helped patients. 

What Bloomberg Intelligence Says:

The failure of Argenx’s trial is unexpected, especially since the company had increased its size to improve the chances of success, and given positive data for the intravenous formulation. The bust likely rules out US approval, and will weigh on consensus’ $4 billion of Vyvgart sales in 2027. 

— Michael Shah, BI pharma analyst

For now, Vyvgart is approved to treat a progressive nerve disease known as myasthenia gravis. Argenx is scheduled to release results from another trial, for the rare blister-causing disease pemphigus vulgaris, toward the end of the year. 

(Updates with analyst comment in seventh paragraph, timing of next study in last)

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