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 etiology 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 Complications Likes to spread to CNS and testes DIC Tumor lysis syndrome rapid breakdown and turnover of lysed cells causes hyperuricemia hyperkalemia hypocalcemia (most common electrolyte abnormality) Prognosis Very responsive to therapy Good prognosis in t(12;21) Worse prognosis in t(9;22)