A 15-year-old girl presents with fever, mucocutaneous bleeding, headache, nausea, and vomiting for 2 weeks. Physical examination reveals generalized lymphadenopathy, hepatomegaly, and splenomegaly. Lab results: PLT 70g/L, WBC 16×10<sup>9</sup>/L, platelets 45×10<sup>9</sup>/L. Bone marrow shows increased blasts, negative peroxidase staining, and granular positivity on glycogen staining. CSF Pandy's reaction is positive. The most likely diagnosis is: