Leukaemia

What it is

Leukaemia is a cancer of the blood-forming tissues in which abnormal white blood cells grow out of control. It is not a single disease but a group of blood cancers that start mainly in the bone marrow, where blood cells are made, and can spill into the bloodstream and other organs. The most important practical distinction is whether it is acute or chronic, because acute leukaemias usually need urgent treatment, while some chronic leukaemias can be monitored for a time before treatment starts.

In leukaemia, immature or abnormal blood cells multiply in a clonal way and crowd out normal marrow function. This can reduce healthy red blood cells, platelets, and infection-fighting white cells. As a result, people may develop tiredness from anaemia, fever or repeated infections, easy bruising or bleeding, bone pain, swollen lymph nodes, or weight loss. Some people are diagnosed only after an abnormal complete blood count.

A simple way to group the main types is shown below:

Main type	Cell line	Usual pace	Typical age pattern
Acute lymphoblastic leukaemia (ALL)	Lymphoid	Fast	More common in children, but also occurs in adults
Acute myeloid leukaemia (AML)	Myeloid	Fast	More common in adults, especially older adults
Chronic lymphocytic leukaemia (CLL)	Lymphoid	Often slower	Mainly older adults
Chronic myeloid leukaemia (CML)	Myeloid	Often slower at first	Mostly adults

In India, diagnosis and treatment are usually guided by haemato-oncology teams using blood counts, bone marrow testing, flow cytometry, cytogenetics, and molecular tests. These tests matter because modern treatment depends heavily on the exact subtype and gene changes.

How it works

Leukaemia develops when a blood-forming cell acquires genetic changes that let it survive, divide, and avoid normal controls. These changes may involve chromosome abnormalities, gene mutations, or fusion genes. The abnormal clone then expands in the marrow and sometimes in blood, lymph nodes, spleen, liver, brain, or testes, depending on the subtype.

The biology differs by type:

1. Acute leukaemias: immature cells called blasts build up quickly and interfere with normal blood production.
2. Chronic leukaemias: more mature-looking abnormal cells accumulate over time, though they still behave abnormally.
3. CML: is strongly linked to the Philadelphia chromosome, which creates the BCR::ABL1 fusion gene, a key treatment target.
4. Many AML and ALL cases: are defined further by molecular markers that affect prognosis and treatment choice.

Most cases do not have a single clear cause. Known risk factors include prior chemotherapy or radiation, certain inherited syndromes, smoking for some myeloid leukaemias, benzene exposure, and increasing age for several adult forms. Evidence also supports a role for random acquired mutations over time. Having a risk factor does not mean a person will develop leukaemia, and many patients have no identifiable cause.

Evidence and uses

Leukaemia is a well-established group of cancers with effective but highly subtype-specific treatments. The main goals are to induce remission, prevent relapse, control symptoms, and improve survival.

Common treatment approaches include:

Treatment	Used in	Purpose
Chemotherapy	Many acute leukaemias	Kill rapidly dividing leukaemia cells
Targeted therapy	CML, some ALL, AML, CLL	Block specific molecular drivers
Immunotherapy	Selected ALL, CLL, others	Help the immune system attack cancer
Stem cell transplant	Higher-risk or relapsed disease	Replace diseased marrow after intensive therapy
Supportive care	All types	Transfusions, antibiotics, tumour lysis prevention, symptom control

Examples of major evidence-based advances include tyrosine kinase inhibitors for CML and molecularly guided treatment in AML and ALL. In CLL, some patients with early, low-burden disease are managed with active surveillance rather than immediate treatment. In acute leukaemias, treatment often starts quickly because delays can be dangerous, especially when there is severe infection, bleeding, or very high white cell counts.

Outcomes vary widely. Some childhood ALL cases are highly curable, while some adult acute leukaemias remain difficult to treat. Prognosis depends on age, subtype, white cell count at diagnosis, chromosome and gene findings, response to initial therapy, and overall fitness.

Diagnosis / how it's measured

Leukaemia is diagnosed using a combination of clinical assessment and laboratory testing. A high or low white blood cell count alone does not confirm leukaemia, and some patients have near-normal counts at presentation.

Typical diagnostic steps include:

1. Complete blood count (CBC) with differential: may show anaemia, thrombocytopenia, abnormal white cell counts, or blasts.
2. Peripheral blood smear: looks at cell appearance under a microscope.
3. Bone marrow aspiration and biopsy: confirms the diagnosis in most cases and estimates blast percentage.
4. Flow cytometry: identifies the cell lineage and immunophenotype.
5. Cytogenetic testing: looks for chromosome changes such as the Philadelphia chromosome.
6. Molecular testing: detects mutations or fusion genes that guide treatment and prognosis.
7. Lumbar puncture or imaging: used in selected cases, especially if spread outside marrow is suspected.

For acute leukaemia, rapid and accurate classification is essential because treatment pathways differ sharply between AML and ALL, and even within those groups. Minimal residual disease testing is increasingly used after treatment to measure how much disease remains at levels too low for routine microscopy.

When to see a clinician

Seek prompt medical care if there is unexplained fever, repeated infections, unusual bruising, bleeding gums, nosebleeds, marked tiredness, pallor, bone pain, swollen glands, or unintentional weight loss. Urgent assessment is especially important if symptoms are severe or come on quickly over days to weeks.

People already diagnosed with leukaemia should contact their treatment team urgently for fever, breathlessness, chest pain, confusion, heavy bleeding, or signs of dehydration. During treatment, even a single fever can be a medical emergency because chemotherapy can cause neutropenia.

Limitations and open questions

Leukaemia is a broad term, and general information can be misleading if it is applied to the wrong subtype. The disease biology, urgency, treatment, and outlook differ greatly between ALL, AML, CLL, and CML, and also within each category.

Research is improving risk stratification, measurable residual disease testing, targeted therapies, and transplant strategies, but important questions remain. Not all patients have targetable mutations, resistance can develop, and access to advanced diagnostics and newer drugs may vary by centre and cost, including in India. Evidence is strong for modern diagnostic classification and subtype-directed treatment, but the best sequence of therapies for some relapsed or high-risk cases is still evolving.