the most common cancer of childhood (peak age 2-5 years),
approximately one-third of all neoplastic diseases in children, and rare in adults
Ionizing radiation, eg X-rays during pregnancy, and Down's syndrome are important associations
B-cell ALL is responsible for ~70-80% of all cases of ALL, whereas T-cell ALL accounts for 15-17% of all cases of ALL.
T-cell ALL often presents as a mediastinal mass that can cause respiratory symptoms, dysphagia, or SVC syndrome.
B-cell ALL usually manifests with fever, malaise, bone and joint pain (esp. lower extremities) and signs of bone marrow failure (pallor, bruising, epistaxis, petechiae, purpura, mucus membrane bleeding)
lymphadenopathy, hepatosplenomegaly and joint swelling
the best diagnostic test = bone marrow aspirate, which shows lymphoblasts
common ALL antigen (CALLA) and terminal deoxynucleotidyl transferase (TdT)
Precursor B-ALL and precursor T-ALL can only be distinguished by immunophenotyping.
The lymphoblasts in precursor B-ALL are TdT+, CD10+ and CD19+, whereas the lymphoblasts in precursor T-ALL express T-cell markers (eg, CD2, CD3, CD4, CD5, CD7 and CD8), TdT and CD1a.