Acute Leukemias

Introduction to Neoplastic Proliferations of White Cells

  • Neoplastic disorders of white cells are predominantly malignant, ranging from aggressive to indolent forms.
  • Hematologic malignancies affect all ages, with around 185,000 new cases diagnosed annually in the U.S.

Classification of White Cell Neoplasms

  • Classification relies on morphologic and molecular criteria, including lineage-specific markers.
  • More than 70 specific entities recognized in the latest World Health Classification.
  • Focus primarily on common malignancies from hematopoietic stem cells, specifically acute leukemias and myeloid neoplasms.

Acute Leukemias

  • Defined as neoplastic proliferations of immature hematopoietic cells (blasts) often replacing normal marrow elements.
  • Classified into three main types:
    • B-Cell Acute Lymphoblastic Leukemia (B-ALL)
    • T-Cell Acute Lymphoblastic Leukemia (T-ALL)
    • Acute Myeloid Leukemia (AML)

Distinctive Features of Acute Leukemias

  • B-ALL:

    • Most common in children (ages 2-10).
    • Symptoms relate to anemia, thrombocytopenia, and neutropenia.

  • T-ALL:

    • Common in adolescents; often involves the thymus.
    • May present with mediastinal masses and similar marrow failure symptoms.

  • AML:

    • Occurs at any stage of life, predominantly in those older than 60.
    • Often arises from preexisting myeloid neoplasms.
    • Symptoms relate to marrow failure and DIC (disseminated intravascular coagulation).

Pathogenesis of Acute Leukemias

  • Common mutations include gene rearrangements and point mutations affecting transcription factors and signaling molecules.
  • Examples:
    • BCR-ABL in B-ALL:
    • 5% of childhood and 25% of adult cases.
    • Forms a fusion gene resulting in active tyrosine kinase leading to poor differentiation.
    • PML-RARA in APL:
    • Associated with retinoic acid receptor dysfunction, can be treated with all-trans retinoic acid (ATRA).
    • IDH1 and IDH2 mutations in AML:
    • Inhibitors can induce differentiation in cases with these mutations.

Clinical Features of Acute Leukemias

  • Symptoms are acute and often include:
    • Fatigue, weakness, fever, and variable white cell counts.
    • Bone pain, lymphadenopathy, splenomegaly (more common in ALL), and potential testicular enlargement.
    • CNS symptoms, particularly in ALL, such as headaches and nausea.

Laboratory Diagnosis

  • Diagnosis of acute leukemia typically requires:
    • Bone marrow biopsy showing > 20% blasts, or blasts in peripheral blood.
    • Immunophenotyping shows lineage-specific markers (e.g., CD10, TdT for ALL; MPO, CD33 for AML).
  • Differential diagnosis between AML and ALL is critical for treatment decisions.

Treatment of Acute Leukemias

  • Treatment generally involves multiple phases:
    • Induction Therapy:
    • Aim to eliminate leukemic cells (e.g., Vincristine, Steroids, Asparaginase).
    • Consolidation Therapy:
    • Further treatment post-remission to eliminate residual disease.
    • Maintenance Therapy:
    • Longer-term, usually for ALL, to sustain remission.
  • The treatment approach can vary significantly between ALL and AML, with favorable prognostic factors improving outcomes greatly in pediatric populations.

Prognostic Factors and Remission Rates

  • Favorable prognosis for childhood B-ALL associated with translocation t(12;21) and lesser leukocyte counts.
  • Poor prognosis associated with the Philadelphia translocation t(9;22) and age extremes.
  • Over 80% of children with B-ALL achieve complete remission with chemotherapy.

Conclusion

  • Acute leukemias represent a serious but treatable group of hematologic malignancies, with ongoing advancements in diagnosis and targeted therapies significantly improving patient outcomes.