What are the different types of leukemia?

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Types of Leukemia

Leukemia is classified into four major categories: acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), chronic lymphocytic leukemia (CLL), and chronic myelogenous leukemia (CML), with additional rare subtypes including acute leukemia of ambiguous lineage and mixed phenotype acute leukemia. 1, 2, 3

Major Acute Leukemia Categories

Acute Myeloid Leukemia (AML)

  • AML is defined by ≥20% myeloid blasts in peripheral blood or bone marrow, encompassing cells of granulocytic, monocyte/macrophage, erythroid, megakaryocytic, and mast cell lineages. 1
  • Key AML subtypes based on genetic and molecular features include: 1
    • Acute Promyelocytic Leukemia (APL): characterized by t(15;17)(q22;q12) translocation creating the PML-RARA fusion gene, representing approximately 10% of all AML cases 1
    • Core Binding Factor AML (CBF-AML): includes AML with t(8;21)(q22;q22), inv(16)(p13.1q22), or t(16;16)(p13.1;q22), representing favorable-risk disease 1
    • AML with normal karyotype: intermediate-risk group where molecular markers (FLT3, NPM1, CEBPα mutations) determine prognosis 1
    • AML with complex karyotype or monosomies: unfavorable-risk disease 1
  • Myeloid leukemia associated with Down syndrome is recognized as a distinct entity by the WHO classification, separate from other AML types due to unique clinical, biological, and genetic features. 4

Acute Lymphoblastic Leukemia (ALL)

  • ALL is divided into B-lymphoblastic leukemia/lymphoma and T-lymphoblastic leukemia/lymphoma based on lineage commitment. 1
  • Diagnostic criteria include ≥25% bone marrow lymphoblasts, though the presence of known recurring cytogenetic abnormalities associated with ALL can lead to diagnosis even with <20% bone marrow blasts. 1
  • Burkitt lymphoma/leukemia is NOT classified as B-ALL, as it represents a mature B-cell neoplasm. 1
  • ALL occurs more often in children compared to other leukemia subtypes. 2, 3

Chronic Leukemia Categories

Chronic Lymphocytic Leukemia (CLL)

  • CLL is the most frequent type of leukemia, typically occurring in older patients with a highly variable clinical course. 5
  • Diagnosis is established by blood counts, blood smears, and immunophenotyping of circulating B-lymphocytes, which identify a clonal B-cell population carrying the CD5 antigen as well as typical B-cell markers. 5
  • Two clinical staging systems (Rai and Binet) provide prognostic information using physical examination and blood counts. 5

Chronic Myelogenous Leukemia (CML)

  • CML is more common in adults and has the highest five-year survival rates among leukemia subtypes. 2, 3

Rare and Ambiguous Leukemia Types

Acute Leukemia of Ambiguous Lineage (ALAL)

  • ALAL encompasses leukemias that either fail to show evidence of lineage commitment or demonstrate commitment to multiple lineages. 1
  • Mixed Phenotype Acute Leukemia (MPAL), formerly called "bilineal" or "biphenotypic" acute leukemia, accounts for 2-5% of all acute leukemias. 1, 6
  • MPAL is characterized by blast cells expressing lineage-defining markers of more than one hematopoietic lineage. 6
  • Specific genetic abnormalities like t(8;21) generally exclude MPAL classification, with exceptions for BCR-ABL1 fusion and MLL rearrangements. 1

MDS/Myeloproliferative Neoplasms (MDS/MPN)

  • This category includes chronic myelomonocytic leukemia (CMML), atypical chronic myeloid leukemia (aCML) BCR-ABL1 negative, and juvenile myelomonocytic leukemia (JMML) as disorders having overlapping dysplastic and proliferative features. 7
  • CMML has been subdivided into proliferative-type (WBC count ≥13 x 10⁹/L) and dysplastic-type (WBC count <13 x 10⁹/L). 7
  • JMML is a rare childhood cancer presenting in infants and young children with peripheral blood monocyte count ≥1 x 10⁹/L, blast percentage <20%, and absence of BCR/ABL1 rearrangement. 7

Clinical Pitfalls and Key Distinctions

A critical pitfall is failing to recognize APL immediately, as it requires immediate ATRA therapy upon clinical suspicion even before genetic confirmation due to high mortality risk. 1

The WHO classification system incorporates cytogenetic data, molecular genetics, immunophenotype, and clinical information to define clinically significant disease entities, making comprehensive diagnostic workup essential. 1

Risk stratification in AML is governed by karyotype and molecular features, with age, initial leukocyte counts, and whether the leukemia is de novo or secondary serving as critical prognostic factors. 1, 8

References

1
Guideline

Acute Leukemia Classification and Diagnosis

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

2
Research

Leukemia: an overview for primary care.

American family physician, 2014

3
Research

Leukemia: What Primary Care Physicians Need to Know.

American family physician, 2023

4
Guideline

Myeloid Leukemia Associated with Down Syndrome

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2025

6
Guideline

Mixed Phenotype Acute Leukemia (MPAL) Diagnostic and Treatment Guidelines

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

7
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

8
Research

Adult acute leukemia.

Current problems in cancer, 1997

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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