The main types of leukemia in children are acute lymphoblastic leukemia (ALL), which accounts for roughly three out of four cases, and acute myeloid leukemia (AML), which makes up most of the rest. Much rarer forms include chronic myeloid leukemia (CML) and juvenile myelomonocytic leukemia (JMML). The type matters because it determines which tests are done, how long treatment lasts, and what the outlook is.
Leukemia is the most common cancer diagnosed in children and adolescents. This guide explains how the types differ, who they affect, and how doctors tell them apart, so families can follow the conversation with their child’s care team.
What Leukemia Is and Why Types Differ
Leukemia is a cancer of the blood-forming tissue, starting in the bone marrow. Our overview of the composition and function of bone marrow explains where this happens. Normally, marrow stem cells mature into red cells, platelets, and several types of white cells in an orderly way.
In leukemia, one early cell acquires genetic changes and begins producing copies that do not mature properly. These abnormal cells crowd the marrow, so fewer healthy blood cells are made. Leukemias are classified by two features:
- Cell lineage: lymphoid (the family that makes lymphocytes) or myeloid (the family that makes granulocytes, monocytes, red cells, and platelets).
- Speed: acute leukemias involve very immature cells called blasts and progress over days to weeks; chronic leukemias involve more mature cells and progress more slowly.
The Main Types of Childhood Leukemia at a Glance
| Type | Share of childhood cases | Typical age | Key features |
|---|---|---|---|
| Acute lymphoblastic leukemia (ALL) | About 75–80% | Peak between ages 2 and 5 | Immature lymphocytes; mostly B-cell type, some T-cell |
| Acute myeloid leukemia (AML) | Most of the remainder | Infancy and teenage years | Immature myeloid cells; several subtypes, including APL |
| Chronic myeloid leukemia (CML) | Small minority | Mostly older children and teens | Driven by the BCR-ABL1 fusion gene (Philadelphia chromosome) |
| Juvenile myelomonocytic leukemia (JMML) | Rare | Usually under age 4 | Overlap of leukemia and myeloproliferative features; linked to RAS pathway genes |
For a broader overview of childhood leukemia, including day-to-day management, see our dedicated guide.
Acute lymphoblastic leukemia (ALL)
ALL is the most common childhood cancer overall. About 85% of cases arise from B-lymphocyte precursors and the rest from T-lymphocyte precursors. T-cell ALL is more common in older boys and often presents with a very high white count or a mass in the chest.
ALL is further divided by genetic features found in the leukemia cells, such as extra chromosomes or specific gene fusions. These features strongly influence how intensive treatment needs to be.
Acute myeloid leukemia (AML)
AML behaves differently from ALL and needs a different, more intensive approach. One subtype, acute promyelocytic leukemia (APL), can cause dangerous bleeding at diagnosis but responds very well to targeted treatment with all-trans retinoic acid and arsenic trioxide. Children with Down syndrome can develop a particular form of AML that is highly treatable with gentler chemotherapy.
Chronic and rare forms
CML in children is managed mainly with oral tyrosine kinase inhibitors, the same class of drugs used in adults; for more on how it is detected, see our guide to diagnosing chronic myeloid leukemia. JMML occurs mostly in toddlers and is associated with conditions such as neurofibromatosis type 1 and Noonan syndrome. It is described in detail in our article on juvenile myelomonocytic leukemia, and the related adult disease in our piece on myelomonocytic leukemia.
A few children have mixed phenotype acute leukemia, in which the cells show both lymphoid and myeloid features. Infant leukemia, diagnosed before the first birthday, is also treated as a distinct group because it often carries rearrangements of the KMT2A gene.
Causes and Risk Factors
In most children, no cause is found, and nothing the parents did or did not do led to the leukemia. Several factors are known to raise the risk:
- Down syndrome, which increases the risk of both ALL and AML.
- Inherited conditions such as Li-Fraumeni syndrome, neurofibromatosis type 1, and certain bone marrow failure syndromes.
- High-dose radiation exposure or previous chemotherapy.
- Having an identical twin with leukemia, especially in early childhood.
More background on leukemia in children, including what is and is not known about causes, is available in our companion article.
Signs and Symptoms
Pediatric leukemia often starts with symptoms that look like common childhood illnesses. The difference is that they persist or keep coming back. Most symptoms reflect a shortage of healthy blood cells or leukemia cells building up in tissues:
- Tiredness and pale skin from anemia.
- Easy bruising, nosebleeds, or tiny red spots (petechiae) from low platelets; unusual bruises, including bruises on the spine, deserve attention.
- Repeated or prolonged fevers and infections.
- Bone or joint pain, sometimes causing a limp or refusal to walk.
- Swollen lymph nodes, or an enlarged liver or spleen causing a swollen tummy.
How the Type Is Diagnosed and Treated
Diagnosing leukemia starts with a complete blood count and a blood smear. If these suggest leukemia, a bone marrow aspirate and biopsy confirm it. The marrow cells then undergo flow cytometry to identify the lineage (lymphoid or myeloid) and genetic testing to find chromosome changes. A lumbar puncture checks whether leukemia cells are in the spinal fluid.
Treatment for childhood leukemia follows standardized protocols, and the type sets the plan. ALL treatment usually lasts two to three years, moving through induction, consolidation, and a long, lower-intensity maintenance phase. AML treatment is more intensive but shorter, and some children need a stem cell transplant.
Newer options include immunotherapies and CAR T-cell therapy for relapsed or resistant B-cell ALL. Our overview of leukemia treatment options compares these approaches.
Outlook has improved greatly over past decades. For ALL, around 90% of children are now cured with modern treatment. AML outcomes are lower but have also improved steadily.
When to See a Doctor
Most bruises, fevers, and leg pains in children are harmless. See your child’s doctor if you notice several symptoms together, or symptoms that do not settle as expected:
- Bruises in unusual places or without injury, or tiny red spots on the skin.
- Pallor and tiredness lasting more than a couple of weeks.
- Fever without a clear cause, or infections that keep returning.
- Bone pain that wakes your child at night or causes limping.
A simple blood count is usually the first step and can quickly rule leukemia in or out.
Frequently Asked Questions
What is the most common type of leukemia in children?
Acute lymphoblastic leukemia (ALL) is by far the most common, accounting for about three-quarters of cases. It most often appears between ages 2 and 5. It is also the most curable form of childhood leukemia.
Is AML in children more serious than ALL?
AML generally requires more intensive treatment and has a lower cure rate than ALL. However, outcomes vary a great deal by subtype. Some forms, such as APL and AML in children with Down syndrome, respond very well.
Do children get chronic leukemia?
Yes, but rarely. Chronic lymphocytic leukemia, the most common adult leukemia, is almost never seen in children. CML does occur in children, mostly teenagers, and is treated with oral targeted drugs.
Can the type of leukemia change over time?
The type is set by the cell of origin and does not usually change. If leukemia relapses, it is typically the same type, although the cells may carry new genetic changes. Doctors repeat testing at relapse to guide the next treatment.
