Snapshot A 7-year-old boy presents with low-grade fever and fatigue. He is notably pale. On physical exam, he has bilateral cervical lymphadenopathy and a mediastinal mass. Blood smear shows increased lymphoblasts. He is referred for a bone marrow biopsy. Introduction Acute leukemia of lymphoid precursor cells that occurs in children Subtypes B-cell ALL – 85% of all ALL t(12;21) most common in children t(9;22) most common in adults same translocation seen in CML CD10+ and CD19/20+ TdT+ (marker of precursor T- and B-cells) T-cell ALL presents in teenagers CD2-8+ (especially CD3+) TdT+ (marker of precursor T- and B-cells) most common presentation is mediastinal mass infiltration of thymus Epidemiology < 15 years most common type of cancer and leukemia in children most cases with no identifiable risk factor Associated conditions Down syndrome in children > 5 years leukemia in Down syndrome children < 5 years = AML Presentation Symptoms most common symptom is fever acute onset recurrent infections bleeding fatigue Physical exam mediastinal mass from infiltration of thymus hepatosplenomegaly lymphadenopathy Evaluation Best initial test - peripheral blood smear ↑ lymphoblasts Most accurate test bone marrow biopsy with cytogenetics ↑ lymphoblasts (> 25%) TdT+, a marker of pre-T and pre-B cells T-cell ALL CD3+ B-cell ALL CD10+ CD19+ negative MPO (myeloperoxidase) CBC reflects bone marrow crowding by neoplasm anemia thrombocytopenia ↓ mature WBCs Differential Diagnosis AML B-cell lymphoma Non-Hodgkin lymphoma Treatment Chemotherapy Prophylaxis to CNS (standard chemotherapy does not penetrate blood-brain barrier) intrathecal chemotherapy Prognosis, Prevention, and Complications Prognosis very responsive to therapy good prognosis in t(12;21) worse prognosis in t(9;22) Complications likes to spread to CNS and testes DIC