Combination Chemotherapy Followed By Donor Stem Cell Transplant in Treating Patients With Hemophagocytic Lymphohistiocytosis

DISEASE CHARACTERISTICS: * Newly diagnosed hemophagocytic lymphohistiocytosis (HLH) meeting 1 of the following criteria\*: * Diagnosis by molecular/genetic methods * Diagnosis by meeting 5 out of 8 of the following criteria: * Clinical criteria: * Fever * Splenomegaly * Laboratory criteria: * Cytopenias affecting ≥ 2 of 3 lineages in the peripheral blood, including the following: * Hemoglobin \< 9.0 g/dL (\< 10.0 g/dL in infants \< 4 weeks of age) * Platelet count \< 100,000/mm\^3 * Neutrophil count \< 1,000/mm\^3 * Hypertriglyceridemia and/or hypofibrinogenemia: * Fasting triglycerides ≥ 3.0 mmol/L (i.e., ≥ 265 mg/dL) * Fibrinogen ≤ 1.5 g/L * Histopathologic criteria: * Hemophagocytosis in bone marrow, spleen, or lymph nodes * No evidence of malignancy * New diagnostic criteria: * Low or absent natural killer (NK) cell activity * Ferritin ≥ 500 mcg/L * Soluble CD25 (i.e., soluble interleukin-2 receptor) ≥ 2,400 U/mL NOTE: \*Patients who do not meet the diagnostic criteria for HLH but who have a strong clinical suspicion of HLH may be eligible at the discretion of the investigator * Primary HLH (i.e., familial hemophagocytic lymphohistiocytosis \[FLH\]) OR secondary HLH (i.e., severe acquired form of HLH) * Acceptable donor meeting 1 of the following criteria: * HLA-identical related donor * Matched unrelated donor * Mismatched unrelated donor …