Shares in Genmab took a hefty hit yesterday after it emerged that Arzerra, which the group is developing together with UK drug giant GlaxoSmithKline, turned in a poor performance in a clinical trial of patients with non-Hodgkin's lymphoma.

The Danish drugmaker saw its stock drop almost 30% on the Copenhagen Stock Exchange after the groups revealed that, disappointingly, just 10% of patients with Rituxan (rituximab) refractory follicular NHL given the highest dose (1000mg) of Arzerra (ofatumumab) responded to treatment with the drug.

Investors in GSK seemed relatively unconcerned by the news, perhaps partly because Genmab stressed a continued commitment to the development of Arzerra in this indication, but it still marks a major setback in the groups’ plans to market the drug as a rival to Roche/Biogen Idec’s blood cancer drug Rituxan, as analysts are expecting that more clinical studies will now need to be carried out to support a marketing application.

The results have also taken their toll on Genmab’s outlook for the year, the absence of expected Arzerra progress-dependent milestones from GSK under the agreement pushing its anticipated operating loss up to 650 million Danish kroner from the originally forecast 400 million Danish kroner.

On the plus side, Genmab announced that for the first six months of the year its revenues grew 26% to 348 million Danish kroner, and that operating losses narrowed 31% to 326 million Danish kroner from the like, year-earlier period.