Used in the treatment of multicentric Castleman disease, a rare lymphoproliferative disorder, in patients who are HIV-negative and HHV-8-negative. It is a monoclonal antibody that targets interleukin-6 (IL-6), a cytokine involved in inflammation and immune response. By neutralizing IL-6, siltuximab helps reduce systemic symptoms such as fever, fatigue, weight loss, and organ enlargement associated with the disease. It is administered intravenously and has shown efficacy in achieving durable tumor and symptom control in clinical studies.