Human herpes virus-8 (HHV-8)-negative or idiopathic multicentric Castleman 
disease (iMCD) is a rare and deadly disorder that sits at the nexus of 
hematology/oncology, virology and immunology. Management of iMCD has been 
challenging due to limited understanding of etiology and pathogenesis and few 
treatment options. The recent approvals in North America, Europe and Brazil of 
siltuximab, a monoclonal antibody against IL-6, for iMCD now provide a safe and 
effective therapy that targets a key aspect of pathogenesis. In the first ever 
randomized, placebo-controlled trial in iMCD, siltuximab significantly reduced 
disease burden and symptoms in a large portion (34%) of patients. The optimal 
dose is 11 mg/kg intravenously every 3 weeks. At this time, duration of 
treatment is often life-long or until treatment failure. Additional research is 
needed to identify biomarkers that may assist with predicting treatment 
effectiveness in iMCD and to investigate the role of siltuximab in 
HHV-8-positive MCD and pediatric iMCD patients.