This is an open-label (all people know the identity of the intervention), multicenter (study conducted in multiple sites), non-randomized (patients are not assigned by chance to treatment groups), Phase 2b study. Up to 75 patients with MCD will be eligible for the study, the majority of whom will be on active therapy with siltuximab at the time of enrollment. Patients will be either siltuximab-naive or have not progressed on siltuximab in the opinion of the investigator. Duration of disease control and survival will be assessed. Data collection for patients who discontinue treatment will be limited to survival, occurrence of malignancies, and subsequent therapies for MCD, which will be assessed twice per year until the patient has been lost to follow up or has withdrawn consent for the study, whichever occurs first. An interim analysis will be conducted (no later than 2 years after the start of enrollment) to further evaluate the benefit and safety of long-term treatment with siltuximab in patients with MCD. A data will occur at 6 years after the start of enrollment and for those patients remaining on treatment after the data cutoff, data collection will be limited to pregnancies and serious adverse events (SAEs), including information on study agent administration and concomitant medications associated with an SAE. Safety evaluations for adverse events, clinical laboratory tests, vital signs, and physical examination will be performed throughout the study. The end of study is the date of the last assessment for the last patient.
