Shares in Genmab A/S opened Tuesday morning down 11 percent on overnight news that its anti-CD20 antibody Arzerra (ofatumumab) failed to demonstrate a progression-free survival (PFS) benefit over Rituxan (rituximab) in a phase III head-to-head study in patients with diffuse large B-cell lymphoma (DLBCL), the most common form of non-Hodgkin's lymphoma (NHL).