Langerhans cell histiocytosis (LCH) is a rare, heterogeneous histiocytic disorder occurring most commonly in children. Because of the rarity of LCH in adults and a lack of prospective randomized trials, the treatment strategy for adults is mostly based on pediatric protocols. The overall response rate of therapy based on vinblastine plus prednisone in adults is lower than in children and the treatment tends to show higher toxicity.There is little data to guide therapy after frontline treatment. In a phase 2 trial, thalidomide as monotherapy gave a 70% response rate in recurrent/refractory low risk LCH but there were no responses in six high risk children. We want to analyze the efficacy and toxicity of thalidomide combined with dexamethasone and cyclophosphamide regimens in the treatment of recurrent/refractory LCH among adult patients at our hospital.

Inclusion Criteria:

• • Histologically confirmed diagnosis of LCH.

  • Patients were recurrent/refractory or at least receive one line of systemic treatment of LCH

  • Age ≥18 years and ≤75 years.

  • LCH involved multisystem or multifocal single system.

  • Eastern Cooperative Oncology Group (ECOG) performance status 0-2.

  • Patients must have adequate renal, liver, and bone marrow function as defined by the following criteria:

    • Absolute neutrophil count ≥1500 cells per mm3 or ≥500 cells per mm3 in the case of known hematopoietic system involvement by LCH.
    • Platelet count ≥100000 cells per mm3 or ≥20000 cells per mm3 in the case of known hematopoietic system involvement by LCH.
    • Creatinine clearance [according to Cockcroft formula] ≥60 mL/min.
    • Aspartate aminotransferase and alanine aminotransferase ≤2·5×upper limit of normal [ULN], and total bilirubin ≤2·5×ULN; or ≤10×ULN in the case of known liver involvement by LCH.

  • No active or untreated infection.

  • No cardiac abnormalities.

  • Subject provide written informed consent.

  • A female is eligible to enter and participate in this study if she is of:

    • Non-childbearing potential including ω Any female who has had a surgical procedure rendering her incapable of becoming pregnant.

ω Subjects have experienced total cessation of menses for more than 1 year and be greater than 45 years in age.

⎫ Childbearing potential, including any female who has had a negative serum pregnancy test within 2 weeks prior to the first dose of study treatment, and agrees to use adequate contraception.

• Male subjects must use an effective barrier method of contraception during the study and for 90 days following the last course of MA if sexually active with a childbearing potential

Exclusion Criteria:

• • Non-langerhans cell histiocytosis.

  • Patients had concurrent malignancies.

  • Patients who were newly diagnosed LCH.

  • History of myocardial infarction, or unstable angina, or New York Heart Association (NYHA) Grade III-IV within 6 months prior to Day 1.

  • Women who were pregnant or of childbearing potential.

  • Known HIV seropositive, active hepatitis C infection, and/or hepatitis B (defined as HCV RNA

    ≥103 copies or HBV DNA ≥103 copies at screening).

  • Major surgical procedure within 28 days prior to the first dose of study treatment.

  • Presence of uncontrolled infection.

  • Evidence of active bleeding or bleeding diathesis.

  • Any serious and/or unstable pre-existing medical, psychiatric, or other condition that could interfere with subject's safety, provision of informed consent, or compliance to study procedures.