Pathology

Pathology/C/10

Precursor T- and B-cell lymphoblastic leukemia/lymphoma

前駆T・Bリンパ芽球性白血病／リンパ腫

タグ
High-yield / ポイント

1. Overview

Precursor B-ALL/LB and T-ALL/LB are aggressive tumors of immature lymphocytes (lymphoblasts).

  • Most common childhood leukemia (80% of pediatric leukemias); peak age ~4 years
  • Manifestation:
    • B-ALL/LB → primarily BM
    • T-ALL/LB → BM and thymus (anterior mediastinal mass)

2. Pathogenesis

  • Closely resembles AML mechanism: block of maturation at early lymphoid differentiation stage
  • Immature blasts accumulate in BM → physical displacement of normal hematopoietic cells → BM failure
  • Block due to mutations in transcription factors regulating lymphoid differentiation:
    • B-ALL/LB: TEL1, PAX5, AML1, BF
    • T-ALL/LB: TAL1, NOTCH1

3. Morphology

  • Blasts represent >25% of marrow cellularity
  • Lymphoblasts: 1–2 nuclei, condensed chromatin, small nucleoli, scant agranular cytoplasm

4. Laboratory findings

  • Variable WBC count, anemia, neutropenia, thrombocytopenia
  • Immunophenotype: CD45dim, TdT, CD19 (B), CD3 (T), CD10
    • TdT (terminal deoxynucleotidyl transferase) is the marker of immaturity in both B- and T-ALL
  • Key genotypes:
    • t(9;22) BCR-ABL (Philadelphia chromosome) → poor prognosis in ALL
    • t(12;21) TEL1/AML1 → most common in pediatric B-ALL; good prognosis
    • TAL abnormalities (T-ALL/LB)
    • Hyper-diploid (>50 chromosomes) → good prognosis

5. Clinical features

  • Abrupt, stormy onset
  • BM suppression symptoms:
    • Fatigue (anemia)
    • Fever/infections (neutropenia)
    • Bleeding (thrombocytopenia)
  • Bone pain and tenderness from marrow expansion
  • Lymphadenopathy, splenomegaly, hepatomegaly (leukemic dissemination)
  • CNS involvement: headache, vomiting, nerve palsies

6. Prognosis

  • Children aged 2–10: ~80% cured
  • Adults: poor prognosis
  • Favorable features: age 2–10, hyperdiploidy, t(12;21), low WBC at presentation
  • Unfavorable: Ph+ (t(9;22)), infant ALL, T-ALL in adults, high WBC

💡 High-yield: ALL = most common childhood cancer. B-ALL → BM; T-ALL → BM + thymus (mediastinal mass). Key marker: TdT (immaturity). Good prognosis: t(12;21), hyperdiploidy, age 2–10. Poor: t(9;22)/Ph+. Symptoms = BM failure triad: anemia + infections + bleeding.