## Epidemiology of Acute Leukemias in Children **Key Point:** Acute lymphoblastic leukemia (ALL) accounts for approximately 75–80% of all childhood acute leukemias, making it the most common hematologic malignancy in children. ### Frequency Distribution | Leukemia Type | Percentage in Children | Peak Age | |---|---|---| | ALL | 75–80% | 2–5 years | | AML | 15–20% | < 2 years, then increases after age 10 | | APL | 5–10% (of AML) | Adolescents and young adults | | AMonoL | < 5% | Rare in children | **High-Yield:** The peak incidence of childhood ALL is between 2–5 years of age. This age group represents the "common ALL" subtype, which carries a relatively favorable prognosis compared to infant ALL (< 1 year) or adolescent ALL (> 10 years). ### Immunophenotypic Subtypes of Childhood ALL - **B-cell ALL (85%):** Most common; includes common ALL (cALL, CD10+) and pre-B ALL - **T-cell ALL (15%):** Associated with older children and worse prognosis - **Burkitt leukemia:** Rare; associated with t(8;14) translocation **Clinical Pearl:** The favorable prognosis in childhood ALL (event-free survival > 85% in modern protocols) contrasts sharply with adult ALL, which has a 5-year survival of only 40–50%. This difference is due to better chemotherapy tolerance in children and the prevalence of favorable cytogenetics (e.g., hyperdiploidy, t(12;21)) in childhood ALL. **Warning:** Do not confuse ALL with lymphoma. ALL is a bone marrow–based disease with circulating blasts; lymphoma is a nodal/extranodal disease. However, Burkitt lymphoma and Burkitt leukemia represent a spectrum of the same disease (t(8;14)).
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