Leukaemia: What Happens When Blood Cell Production Goes Wrong

Leukaemia is a cancer of blood-forming cells. In most forms, the disease begins in the bone marrow, where blood cells are normally produced and matured before entering the circulation.

Haematopoietic stem cells give rise to two broad cell lineages. The myeloid lineage produces red blood cells, megakaryocytes and platelets, neutrophils, eosinophils, basophils and monocytes. The lymphoid lineage produces B and T lymphocytes.

Normally, developing blood cells move through tightly controlled stages of proliferation, differentiation and maturation. In leukaemia, one clone acquires genetic changes that allow it to survive and expand abnormally. In some leukaemias the cells remain very immature. In others they resemble more mature blood cells but are still abnormal in number or function.

As the malignant clone expands, normal marrow production can be suppressed. The result may be anaemia, thrombocytopenia and impaired immunity, sometimes all at once. Leukaemic cells may also circulate in the blood or accumulate in tissues such as the lymph nodes and spleen.

The blood count reflects marrow failure as well as tumour burden

The characteristic blood-count abnormalities of leukaemia reflect both the malignant clone and the loss of normal blood-cell production.

If red-cell production falls, haemoglobin may fall and the patient can become anaemic. Tiredness, pallor, dizziness, tachycardia and exertional breathlessness can follow. If platelet production is reduced, thrombocytopenia can lead to petechiae, bruising, gum bleeding, epistaxis or heavier menstrual bleeding. If normal neutrophil production is impaired, infection risk rises.

Those abnormalities may appear together because the underlying problem is occurring in one shared site: the marrow.

A high white-cell count does not necessarily mean a patient has strong immunity. Many circulating cells may be malignant, immature or functionally abnormal. Conversely, some patients with acute leukaemia have a normal or low total white-cell count at diagnosis. A single white-cell number therefore does not rule leukaemia in or out.

The differential count, haemoglobin, platelets, neutrophils, blood film and trend over time all matter. In acute leukaemia, blasts may appear in the peripheral blood, but they do not have to be present in large numbers for serious marrow disease to exist.

Leukaemic cells can also accumulate outside the marrow. Lymphadenopathy and splenomegaly are common in some lymphoid leukaemias, and hepatosplenomegaly can be seen in acute disease. Bone or joint pain can occur when abnormal cells expand within the marrow cavity, particularly in children with acute lymphoblastic leukaemia.

The name tells you two things: pace and lineage

The first part of the name, acute or chronic, tells you something about the biology and usual pace of the disease. The second part, myeloid or lymphoid, tells you which developmental lineage the abnormal clone belongs to.

Acute leukaemias usually involve precursor cells with impaired maturation. The abnormal cells can accumulate rapidly and symptoms often develop over days or weeks. Treatment commonly needs to begin promptly.

Chronic leukaemias usually involve cells that are further along their developmental pathway and often progress more slowly. Some patients are diagnosed incidentally on routine blood testing before they feel unwell.

This produces four broad groups: acute myeloid leukaemia (AML), acute lymphoblastic leukaemia (ALL), chronic myeloid leukaemia (CML) and chronic lymphocytic leukaemia (CLL).

The names are useful, but they are only the starting point. Modern classification increasingly depends on genetics as well as cell appearance. In AML in particular, some genetic abnormalities can define a disease entity, so the old idea that diagnosis is simply based on one blast percentage is too simplistic. Morphology, immunophenotype and molecular findings now belong together.

The four common leukaemias are biologically different diseases

Acute myeloid leukaemia (AML) arises from the myeloid lineage and becomes more common with increasing age, although it can occur at any age. The disease is genetically heterogeneous. Different chromosomal changes and mutations define important subtypes and influence prognosis and treatment. This is why two patients both described as having AML may receive different treatment plans.

One AML subtype deserves particular attention: acute promyelocytic leukaemia (APL). It is usually associated with the PML::RARA fusion created by a translocation involving chromosomes 15 and 17. APL can cause a severe coagulopathy with both bleeding and thrombosis, so suspected APL requires urgent specialist management. It is also a striking example of targeted therapy because all-trans retinoic acid and arsenic-based treatment can drive abnormal promyelocytes towards differentiation.

Acute lymphoblastic leukaemia (ALL) arises from lymphoid precursor cells, most often B-lineage and less commonly T-lineage. It can occur at any age but has a strong childhood peak and is the most common leukaemia in children. Malignant lymphoblasts accumulate in the marrow and may also circulate in the blood or infiltrate lymph nodes, liver, spleen, the central nervous system or other tissues. Clinical features often reflect marrow failure, with anaemia, bruising or bleeding and infection, alongside lymphadenopathy, hepatosplenomegaly or bone pain in some patients. The possibility of central nervous system involvement is one reason ALL treatment includes CNS-directed therapy.

Chronic myeloid leukaemia (CML) is biologically distinct because it is driven by BCR::ABL1, usually created by the Philadelphia chromosome translocation between chromosomes 9 and 22. The resulting protein is a continuously active tyrosine kinase that drives abnormal myeloid-cell proliferation. Tyrosine kinase inhibitors changed the natural history of CML by targeting that signal directly, making it one of the clearest examples of molecularly targeted cancer treatment.

Chronic lymphocytic leukaemia (CLL) is usually a malignancy of mature B lymphocytes and mainly affects older adults. It may be discovered incidentally after lymphocytosis is found on a routine blood test. Some people remain well for years without needing treatment. Active monitoring is not neglecting the cancer. It avoids exposing an asymptomatic patient to treatment before there is a clinical reason to start it.

When CLL does require treatment, current UK practice is now dominated by targeted agents. The 2025 British Society for Haematology guideline describes BCL2 inhibitors and Bruton tyrosine kinase inhibitors as central treatment options and notes that these targeted approaches have largely superseded chemoimmunotherapy.

Diagnosis is built from several layers of evidence

A full blood count may be the first clue, but it cannot tell you the complete diagnosis. A blood film can reveal abnormal morphology, immature cells or a characteristic lymphocytosis, but modern haematology does not classify leukaemia from appearance alone.

For suspected acute leukaemia, bone marrow aspiration and trephine biopsy are commonly used to assess the marrow directly. Flow cytometry examines patterns of cell-surface and intracellular markers and helps determine lineage and stage of maturation. Cytogenetic testing looks at chromosome abnormalities. Molecular testing identifies fusion genes and mutations that may define the disease, refine risk and point towards targeted treatment.

The British Society for Haematology specifically recommends a combined diagnostic approach for AML using clinical features, morphology, immunophenotyping and genetic evaluation. That integrated approach matters because molecular information increasingly determines how the disease is named and treated.

CML is confirmed by demonstrating BCR::ABL1. CLL is often diagnosed from peripheral blood findings and flow cytometry without needing a marrow biopsy simply to establish the diagnosis. ALL and AML generally need more extensive marrow and molecular assessment.

After treatment begins, testing does not stop. Many patients with acute leukaemia are monitored for measurable residual disease, sometimes shortened to MRD. These tests look for very small amounts of disease that remain below the level visible on routine microscopy. MRD results can help specialists judge depth of response and risk of relapse.

Modern response assessment can therefore detect disease below the level visible on routine microscopy by looking for a specific abnormal cell population or molecular marker.

Treatment depends on subtype, genetics and disease behaviour

There is no single “leukaemia treatment”. Therapy depends on the exact disease, genetic findings, age, general health, treatment goals and previous response.

AML may be treated with intensive chemotherapy, lower-intensity treatment, targeted medicines and, for selected patients, allogeneic stem-cell transplantation. ALL treatment is usually delivered in phases and commonly combines corticosteroids and chemotherapy, with targeted medicines or immunotherapy used in some disease subtypes or relapse settings. Treatment also needs to address disease risk within the central nervous system.

CML is usually treated with tyrosine kinase inhibitors directed at BCR::ABL1. CLL may be observed for a period without treatment, then treated with targeted agents when symptoms, progression or other clinical indications develop.

Whatever the anti-leukaemia treatment, the patient's normal marrow may be severely suppressed by the disease, the treatment or both. This is why supportive care is not an optional extra. It is part of the treatment pathway.

Red-cell transfusion may be needed for symptomatic anaemia. Platelet transfusion may be required when thrombocytopenia creates significant bleeding risk. Infection prevention and prompt antimicrobial treatment are crucial when neutrophils are low. Central venous access needs careful assessment because the line that enables treatment can also become a route for infection or thrombosis.

Rapid tumour-cell breakdown can also cause tumour lysis syndrome. Potassium and phosphate can rise, calcium may fall and urate can increase, creating a risk of arrhythmia, seizures and acute kidney injury. Patients at risk may therefore need prophylaxis, hydration and close biochemical monitoring according to specialist protocols.

In patients receiving venetoclax, for example, UK safety guidance specifically emphasises tumour-lysis risk assessment, preventive measures and laboratory monitoring. The important nursing point is to understand why apparently routine fluid balance, renal function and electrolyte results can become time-critical around the start of treatment.

What matters at the bedside

Leukaemia nursing is often about recognising what a changing blood count means for the person in front of you.

A new temperature or signs of infection in a neutropenic patient require urgent assessment. NICE describes suspected neutropenic sepsis as an acute medical emergency. Infection may also look less dramatic than expected in someone who is severely immunosuppressed, so deterioration should not be dismissed because the classic inflammatory response is absent.

Bleeding risk needs the same attention. New petechiae, mucosal bleeding, haematuria, melaena or unexpectedly heavy menstrual bleeding may reflect severe thrombocytopenia. A new severe headache or neurological change in a patient with very low platelets is especially concerning because intracranial bleeding is a possible emergency.

Anaemia may explain fatigue, tachycardia or breathlessness, but it should not become an automatic explanation for every symptom. Infection, pulmonary embolism, bleeding and treatment complications still need clinical assessment.

Patients may also be dealing with mucositis, nausea, altered taste, poor intake, diarrhoea, constipation, sleep disruption and profound fatigue. These are not peripheral issues. They can affect hydration, nutrition, treatment tolerance and quality of life.

Some complications arise from a very high circulating leukaemic-cell burden rather than marrow failure alone. Hyperleukocytosis can impair microvascular blood flow and, in severe cases, cause leukostasis with neurological or respiratory symptoms. This is most often associated with acute leukaemias and requires urgent specialist assessment.

At the bedside, the key is to connect symptoms and laboratory results back to the disease process: which normal cell lines are suppressed, how large the malignant burden is, where leukaemic cells may be infiltrating, and what treatment is doing to both malignant and healthy cells.

Summary

Leukaemia is a group of haematological cancers in which an abnormal blood-cell clone expands within the marrow and, depending on the disease, the blood and other tissues. The consequences come from both the malignant cells themselves and from suppression of normal haematopoiesis.

Acute leukaemias usually involve immature precursor cells and progress quickly. Chronic leukaemias generally involve more mature abnormal cells and may progress more slowly. Myeloid and lymphoid describe the developmental lineage involved.

AML, ALL, CML and CLL are therefore not four versions of one disease. They differ in age distribution, cell of origin, genetics, treatment and clinical course. Diagnosis now combines blood counts and morphology with flow cytometry, cytogenetics and molecular testing, while treatment is increasingly matched to the biology of the abnormal clone.

For nurses, the central clinical pattern remains simple and important: marrow failure can produce anaemia, thrombocytopenia and impaired immunity at the same time. Recognising what those changes mean for bleeding, infection, oxygen delivery and treatment complications is a large part of safe day-to-day care.

References

British Society for Haematology (2020) Guideline on the diagnosis and management of chronic myeloid leukaemia. Available at: https://b-s-h.org.uk/guidelines/guidelines/guideline-on-the-diagnosis-and-management-of-chronic-myeloid-leukaemia

British Society for Haematology (2022) Recommendations for laboratory testing of UK patients with acute myeloid leukaemia: a British Society for Haematology good practice paper. Available at: https://b-s-h.org.uk/guidelines/guidelines/recommendations-for-laboratory-testing-of-uk-patients-with-acute-myeloid-leukaemia-a-british-society-for-haematology-good-practice-paper

British Society for Haematology (2025) British Society for Haematology guideline for the treatment of chronic lymphocytic leukaemia. Available at: https://b-s-h.org.uk/guidelines/guidelines/2025-british-society-for-haematology-guideline-for-the-treatment-of-chronic-lymphocytic-leukaemia

Khoury, J.D. et al. (2022) ‘The 5th edition of the World Health Organization Classification of Haematolymphoid Tumours: Myeloid and Histiocytic/Dendritic Neoplasms’, Leukemia, 36(7), pp. 1703–1719. Available at: https://pubmed.ncbi.nlm.nih.gov/35732831/

National Institute for Health and Care Excellence (NICE) (2012, updated) Neutropenic sepsis: prevention and management in people with cancer (CG151). Available at: https://www.nice.org.uk/guidance/cg151

National Institute for Health and Care Excellence (NICE) (2016) Haematological cancers: improving outcomes (NG47). Available at: https://www.nice.org.uk/guidance/ng47

NHS (n.d.) Acute lymphoblastic leukaemia. Available at: https://www.nhs.uk/conditions/acute-lymphoblastic-leukaemia/

NHS (n.d.) Acute myeloid leukaemia. Available at: https://www.nhs.uk/conditions/acute-myeloid-leukaemia/

NHS (n.d.) Chronic lymphocytic leukaemia. Available at: https://www.nhs.uk/conditions/chronic-lymphocytic-leukaemia/

NHS (n.d.) Chronic myeloid leukaemia. Available at: https://www.nhs.uk/conditions/chronic-myeloid-leukaemia/