In patients with Rosai-Dorfman disease (RDD), a treatment regimen of lenalidomide combined with dexamethasone is planned to be used.

Patients received oral lenalidomide 25mg on days 1-21 and dexamethasone 40mg on days 1, 8, 15, 22, in 28-day cycles for 12 total cycles.

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.