The objective of this study is to determine the incidence of complete and partial response and the duration of response in patients with Langerhans Cell Histiocytosis (LCH) treated with sequential administration of oral 6-Thioguanine (6-TG) after Methotrexate (MTX).

• Drug: Methotrexate
• Drug: 6-Thioguanine
• Drug: Leucovorin Calcium

Inclusion Criteria:

• Patients with histologic proof of LCH who have multifocal or multisystem disease involvement.
• Patients must have a life expectancy of at least 8 weeks.
• All patients must have ECOG performance level rating of-< 2.
• Patients or their parents (guardian) must sign an informed consent indicating that they are aware of the investigational nature of the study, using commercially available drugs.
• Patients must have recovered from the toxic effects of prior therapy before entering this study or at least 2 weeks should have elapsed since the end of last course of chemotherapy.
• Patients must have adequate liver function (bilirubin _< 2.0 mg/dl, SGOT less than 1.5 times normal (unless it is due to disease), adequate renal function (creatinine <_ 1.5 mg/dl, creatinine clearance >_ 60 ml/min/1.73 m2) and normal electrolytes.
• Patients should have a granulocyte count > 500/uL and a platelet count >_ 100,000/uL (unless due to disease involvement of the bone marrow).
• Male and female patients of child-bearing age should use effective methods of contraception, if sexually active.

Exclusion Criteria:

• Patients with active infections or significant medical conditions other than their disease (LCH) shall be excluded.