Study of Clofarabine in Patients With Recurrent or Refractory Langerhans Cell Histiocytosis and LCH-related Disorders

Inclusion Criteria: * Prior diagnosis of Langerhans Cell Histiocytosis (stratum 1) or LCH-related disorder (stratum 2) established by standard diagnostic criteria and confirmed histologically. * Evidence of active disease (histological confirmation of reactivation or progression is not required). * Performance Score \> 70% (use Lansky score for age \< 16 and Karnofsky score for age = \>16). * Patients of all ages will be eligible. * Provide signed written informed consent. * In stratum 1, patients must have failed one prior systemic chemotherapy regimen. In stratum 2, RDD patients must have failed treatment with corticosteroid. ECD patients who have confirmed BRAF V600E mutation must have failed treatment with a BRAF inhibitor or are not considered to be eligible for such treatment. * There is no limitation of amount or the type of prior therapy or drugs. * Female patients of childbearing potential must have a negative serum pregnancy test within 14 days prior to enrollment. Male and female patients must use an effective contraceptive method during the study and for a minimum of 6 months after study treatment. * Capable of understanding the investigational nature, potential risks and benefits of the study, and able to provide valid informed consent. * Participants must have adequate marrow functions as defined below, except those with involvement of hematopoietic system for whom these criteria can be waived: * Absolute neutrophil count ≥ 750 cells/µL * Platelets ≥75,000…