Acute lymphoblastic leukemia (ALL)

Synonyms: acute lymphocytic leukemia, childhood leukemia, blood cancer, B-ALL, T-ALL
Specialty: Internal medicine · Haematology & oncology
Images: Blood smear & cytology 3
Last updated: 10/2026 · Dr. Pascal Bafteh

Contents

Images (3)
Definition
Classification
Occurrence & epidemiology
Aetiopathogenesis
Clinical features
Diagnosis
Keep learning in the app
Further reading (open access)
Cross-references

Images (3)

Acute lymphoblastic leukemia (ALL) – Bone marrow smear in ALL: densely packed lymphoblasts with a high nuclear-cytoplasmic ratio and scant basophilic cytoplasm — Bone marrow smear in ALL: densely packed lymphoblasts with a high nuclear-cytoplasmic ratio and scant basophilic cytoplasmImage: Animalculist (Wikimedia Commons) · CC BY-SA 4.0 · Source

Acute lymphoblastic leukemia (ALL) – Peripheral blood smear in ALL: several lymphoblasts with fine chromatin and little cytoplasm — Peripheral blood smear in ALL: several lymphoblasts with fine chromatin and little cytoplasmImage: SpicyMilkBoy (Wikimedia Commons) · CC BY-SA 4.0 · Source

Acute lymphoblastic leukemia (ALL) – Blood smear of a child with ALL (Pappenheim stain): three large lymphoblasts among the red cells — Blood smear of a child with ALL (Pappenheim stain): three large lymphoblasts among the red cellsImage: Christaras A (Wikimedia Commons) · CC BY 2.5 · Source

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Definition

Acute lymphoblastic leukemia (ALL) is a malignant disease of lymphoid precursor cells. Uncontrollably proliferating lymphoblasts displace normal hematopoiesis and may infiltrate the central nervous system and the testes. ALL is the most common cancer in childhood but occurs at any age.

Classification

By cell lineage: B-lymphoblastic leukemia/lymphoma (B-ALL/LBL) and T-lymphoblastic leukemia/lymphoma (T-ALL/LBL).
The term leukemia is used when blood and bone marrow are involved, lymphoblastic lymphoma when involvement is mainly extramedullary.
The WHO classification additionally considers genetic features, clinical presentation, morphology, and immunophenotype.

Occurrence & epidemiology

About 60 % of all ALL cases occur in children. Incidence peaks at age 2 to 5 years, with a second peak after age 50. In children, ALL accounts for about 75 % of all leukemias.

Aetiopathogenesis

The cause is a series of acquired genetic aberrations in a lymphoid precursor cell. Risk factors are ionizing radiation, certain chemicals such as benzene, and congenital syndromes such as Down syndrome, Fanconi anemia, Bloom syndrome, and ataxia-telangiectasia.

Typical cytogenetic abnormalities:

t(9;22)/BCR::ABL1 (Philadelphia chromosome): in about 25 % of adults, about 5 % of children
High hyperdiploidy (51–65 chromosomes): about 25 % of children
t(12;21)/ETV6::RUNX1: 20–25 % of children
Hypodiploidy: about 5 %

Clinical features

Symptoms are often present for only days to weeks before diagnosis:

Anemia: fatigue, weakness, pallor, exertional dyspnea, tachycardia
Thrombocytopenia: petechiae, bruising, nose and gum bleeding, mucosal bleeding
Granulocytopenia: fever and severe or recurrent infections
Organ infiltration: enlargement of the liver, spleen, and lymph nodes
Bone and joint pain from bone marrow and periosteal infiltration, especially in children
CNS involvement is common: cranial nerve palsies, headache, visual and auditory symptoms, altered mental status

Diagnosis

Blood count and smear: pancytopenia with peripheral blasts; blasts up to 90 % of white cells. The white cell count is increased in about half of patients and normal or low in the other half.
Bone marrow: diagnosis at ≥ 20 % lymphoid blasts among nucleated cells; typical blast count 25–95 %.
Auer rods are never present in ALL.
Cytochemistry: terminal deoxynucleotidyl transferase (TdT) positive in lymphoid cells.
Immunophenotyping: CD19, CD20, and CD22 in B-cell origin, CD3 in T-cell origin.
Cytogenetics and molecular genetics, e.g., detection of BCR::ABL1.

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