Efficacy and Safety of the RD Regimen(Lenalidomide, Dexamethasone) for Rosai-Dorfman Disease

Inclusion Criteria: * Definitively diagnosed adult RDD patients; * Aged between 18 and 80 years; * Treatment-naive or refractory/relapsed; * ECOG performance status score ≤ 2; * Judged by clinicians as suitable for treatment with this protocol; * Patients or their families able to understand the study protocol and willing to participate in the study, providing written informed consent. Exclusion Criteria: * Subjects who have undergone major surgery within 4 weeks prior to the first dose of the study; * Subjects who have received radiotherapy within 4 weeks prior to the first dose of the study; * Subjects with a history of myocardial infarction within the past year; * Patients with New York Heart Association (NYHA) Class 3 or 4 congestive heart failure, or a history of NYHA Class 3 or 4 congestive heart failure; * Pregnant or lactating women; * Patients who cannot strictly practice contraception after participating in the study; * Abnormal liver and kidney function: creatinine level ≥176.8 μmol/L (2 mg/dL), transaminase and bilirubin levels more than 2 times the upper limit of normal * Abnormal blood counts: absolute neutrophil count less than 1×10\^9/L, platelet count less than 50×10\^9/L; * Patients or their families who cannot understand the conditions and objectives of the study; * Any other situation where the investigator considers the patient unsuitable to participate in this trial.