Sirolimus in Previously Treated Idiopathic Multicentric Castleman Disease

Inclusion Criteria: * Male or female, age 2-80 * Documented disease history consistent with the diagnostic criteria for iMCD * Failed/refractory (patient did not achieve sufficient disease control with anti-IL-6 therapy, as determined by the site investigator), relapsed (return of symptoms while on therapy), or inability to tolerate anti-IL-6 or anti-IL-6 receptor therapy * Evidence of active disease, defined as at least two abnormalities in the criteria comprising the CBR criteria, including at least one objective measurement (hemoglobin, weight loss, or lymph node size) * Ability to consume oral medication in the form of a tablet * Ability to provide, or for a legally authorized representative to provide on their behalf, informed consent prior to any study-specific activities Exclusion Criteria: * Subjects cannot be pregnant or nursing females * Except for anti-IL6 blockade therapy (siltuximab or tocilizumab), the last dose of which must be ≥ 14 days prior to enrollment (unless subjects cannot or are unwilling to undergo a 14 day washout period), subjects cannot have received any systemic therapy(ies) intended to treat iMCD other than corticosteroids within 28 days of enrollment * Subjects cannot have previously received sirolimus monotherapy to treat iMCD * Subjects cannot have any of the following: ECOG \>3 (or Karnofsky/Lansky score ≤ 60 in children); Estimated glomerular filtration rate (eGFR) \< 30 mL/min/1.73 m2 or creatinine \> 3.0 mg/dL; Absolute neutrophil count…