Evaluation of Efficacy and Tolerance of Cladribine in Symptomatic Pulmonary Langerhans Cell Histiocytosis

Inclusion Criteria: * Age 16 to 55 yr * Histologically proven pulmonary Langerhans cell histiocytosis ( patients with presumptive diagnosis whose lung function precludes lung biopsy may be included after revision of their medical record at the national reference center for Langerhans cell histiocytosis) * Symptomatic pulmonary Langerhans cell histiocytosis (NYHA dyspnea class ≥2) with: * irreversible airflow obstruction (FEV1/FVC\<70%) with postbronchodilator FEV1 comprised between 30 and 70% of predicted * and/or decrease ≥15% in FEV1, FVC or DLCO as compared to baselines values in the year preceding the inclusion * Signed written informed consent Exclusion Criteria: * Women at childbearing age without adequate contraception or wishing breastfeeding * Male without adequate contraception during the study * Dyspnea due to severe pulmonary arterial hypertension (PAP≥35mmHg) confirmed by cardiac right catheterism * Previous malignancy * Current infectious disease * Renal failure * Liver failure * Severe alteration of lung * Hematologic disease unrelated to Langerhans cell histiocytosis * Epilepsy * Hepatic, spleen or hematology involvement by Langerhans cell histiocytosis * Pneumothorax within a month previously to inclusion * Previous treatment with cladribine * Contra indication to the use of cladribine * Previous myelosuppressive treatment * Simultaneous participation to another interventional clinical trial