Leukemia
What is leukemia?

Leukemia is a general term for a group of cancers affecting blood-forming cells in the bone marrow. In leukemia, abnormal white blood cells are produced. In acute forms, these cells are usually immature. In chronic forms, they may appear more mature but grow or function abnormally. Over time, leukemic cells can accumulate and interfere with normal blood cell production. This can cause anemia, infections, bleeding, and other complications.

How does leukemia develop?

Blood cells are normally produced in the bone marrow from hematopoietic stem cells. As they develop, these cells branch into two main lineages:

The myeloid lineage, which produces red blood cells, platelets, granulocytes (neutrophils, eosinophils, and basophils), and monocytes.
The lymphoid lineage, which produces B lymphocytes, T lymphocytes, and natural killer (NK) cells.

Cells in each lineage pass through several stages of maturation before they become functional. Cells in the earliest, still immature stages are called blasts. Blasts do not normally circulate in the peripheral blood.

Leukemia develops when genetic changes (mutations) in a blood-forming cell disrupt the normal control of its growth, maturation, and survival. Depending on the type of leukemia, this may happen in a stem cell or in a cell at a later stage of development. A single altered cell gives rise to a group of abnormal cells that multiply uncontrollably or survive longer than they should. They accumulate in the bone marrow and often in the blood, gradually interfering with normal blood production. Reduced red blood cell production causes anemia. A shortage of functional white blood cells increases the risk of infection. Reduced platelet production increases the risk of bleeding.

Types and classification of leukemia

Leukemias are classified by how quickly they progress (acute or chronic) and which cell lineage they affect (myeloid or lymphoid). Combining these characteristics gives four main types:

ALL – acute lymphoblastic leukemia affects lymphoid precursor cells. It progresses quickly and is the most common form of leukemia in children, although it also occurs in adults.
AML – acute myeloid leukemia is a diverse group of myeloid leukemias that usually progress quickly. They are further classified according to genetic changes.
CLL – chronic lymphocytic leukemia affects more mature B cells and often progresses slowly.
CML – chronic myeloid leukemia is characterized by overproduction of cells in the myeloid lineage and is associated with the BCR::ABL1 genetic change.

Other, rarer forms also exist.

According to their course, leukemias are described as:

Acute leukemias – immature cells (blasts) accumulate rapidly, and the disease usually progresses quickly. Prompt diagnosis and treatment are needed.
Chronic leukemias – these usually develop more slowly and may cause no symptoms for a long time. Some are discovered during a routine blood test.

Main causes and risk factors

The exact cause of leukemia is unknown in most cases. It develops when genetic changes (mutations) in blood-forming cells disrupt the normal control of their growth, maturation, and survival, leading to the multiplication of abnormal cells.

Leukemia is not contagious and cannot pass from one person to another. Some factors are associated with a higher risk, however. Having a risk factor does not mean a person will develop leukemia, and many people with leukemia have no known risk factors.

Age and sex. The risk of certain types of leukemia increases with age; AML and CLL occur more often in older adults. Men develop leukemia slightly more often than women.
Inherited genetic conditions and family history. Certain inherited conditions, including Down syndrome, Fanconi anemia, and Li-Fraumeni syndrome, increase the risk. More rarely, inherited genetic changes make members of some families more susceptible to leukemia. First-degree relatives of people with CLL have a somewhat higher risk.
Environmental exposures and previous treatments. Exposure to benzene or radiation, smoking (particularly for AML), and previous chemotherapy or radiation therapy for another condition may increase the risk.
Previous bone marrow disorders. Myelodysplastic syndromes (MDS) and certain other blood disorders may develop into leukemia over time.

What are the symptoms of leukemia?

Signs and symptoms vary according to the type and course of the disease. Many are nonspecific and can also occur with more common conditions. Having these symptoms does not necessarily mean a person has leukemia; diagnosis requires a medical assessment and appropriate tests.

Reduced numbers of normal blood cells

Anemia – fatigue, weakness, dizziness, pale skin, and shortness of breath.
Reduced numbers or ineffective functioning of white blood cells – fever and frequent or recurring infections.
Thrombocytopenia – easy bruising, unexplained or prolonged bleeding, petechiae (small red spots on the skin), and bleeding from the nose or gums.

Accumulation of leukemic cells

Swollen lymph nodes, bone or joint pain, and enlargement of the spleen or liver may occur. An enlarged spleen or liver can cause a feeling of fullness or discomfort under the ribs.

General symptoms

These may include fever, night sweats, loss of appetite, and unexplained weight loss.

How do symptoms differ by type?

Acute leukemias – symptoms can develop over days or weeks and usually become noticeable quickly. In ALL, particularly in children, bone pain and enlargement of the lymph nodes or spleen may occur. In acute promyelocytic leukemia (APL), a distinct form of AML, bleeding can be severe and requires urgent treatment.
Chronic leukemias – these may cause no symptoms for months or years and may be discovered through a blood test. CLL may cause painless swelling of lymph nodes in the neck, armpits, or groin. In CML, an enlarged spleen may cause early fullness after eating or a feeling of heaviness under the left ribs.

Warning signs and urgent care

Seek a medical assessment if fatigue, paleness, fever, infections, bruising, bleeding, or unexplained weight loss persist or worsen. A complete blood count is often the first step, but it cannot establish the diagnosis on its own.

Seek immediate medical attention for bleeding that does not stop, severe difficulty breathing, fainting or confusion, sudden severe pain, or fever with rapid deterioration, particularly during chemotherapy or when neutrophil levels are low.

How is leukemia diagnosed?

Diagnosis is based on a combination of clinical assessment and tests.

Medical history and physical examination

The doctor reviews symptoms, how long they have been present, and the person’s medical history. The examination may look for pale skin, bruising, swollen lymph nodes, or an enlarged spleen or liver.

Complete blood count (CBC)

A CBC counts red blood cells, white blood cells, and platelets. It may show a very high or very low white blood cell count, as well as reduced platelet and red blood cell counts.

Microscopic examination of peripheral blood

This may reveal changes in the appearance of blood cells and the presence of abnormal or immature cells.

Bone marrow examination

Bone marrow aspiration and biopsy allow the marrow cells to be assessed. They are important tests for confirming and classifying most leukemias.

The bone marrow sample may be examined further using:

Morphology and immunophenotyping – help identify the type, lineage, and maturity of abnormal cells.
Karyotyping and FISH – identify certain chromosomal changes.
Molecular tests, such as next-generation sequencing (NGS) – identify genetic changes relevant to diagnosis, classification, treatment selection, and, in some cases, disease monitoring.

Other tests: Additional laboratory and imaging tests may be performed according to the type of leukemia, symptoms, complications, and treatment-planning needs.

How is leukemia treated?

Treatment is directed by a hematologist. It depends on the leukemia subtype, its genetic features, the patient’s age and overall health, and whether the disease is newly diagnosed, has returned, or is refractory (does not respond to treatment). Identifying the exact subtype is therefore important when choosing treatment. The main approaches are:

Chemotherapy

These medications destroy cancer cells or prevent them from dividing. For acute leukemias, chemotherapy is often given in phases: induction (to achieve remission), consolidation (to reduce the risk of relapse), and, in some treatment plans, maintenance therapy.

Targeted therapy

These medications act on specific mechanisms in leukemic cells. An example is oral tyrosine kinase inhibitors (TKIs) used for CML.

Immunotherapy

These treatments use the immune system to fight cancer. They include monoclonal antibodies and, in selected cases, CAR T-cell therapy.

Stem cell transplantation

After preparatory treatment, blood-forming cells are replaced with healthy cells, usually from a donor (an allogeneic transplant). An autologous transplant is used less often, in particular circumstances.

Active monitoring

For some people with CLL who have no symptoms or signs of progression, the hematologist may monitor the disease through regular assessments and begin treatment when needed.

Treatment also varies by subtype:

ALL and AML

Treatment usually begins promptly and may be divided into induction, consolidation, and, depending on the treatment plan, maintenance. Chemotherapy, targeted therapies, immunotherapy, and transplantation may be used.

CML

Oral tyrosine kinase inhibitors (TKIs) are the main treatment. Taking the medication regularly and undergoing molecular monitoring are important. Carefully supervised discontinuation may be considered only for selected patients.

CLL

Some patients undergo active monitoring with regular tests. When treatment is needed, targeted therapies, monoclonal antibodies, chemotherapy, or combinations of these may be used. Transplantation is reserved for particular cases.

Treatment options may include other medications, immunotherapy such as CAR T-cell therapy in selected cases, transplantation, or participation in a clinical trial.

Supportive care accompanies treatment throughout. It includes transfusions when needed, prevention and treatment of infections, and symptom control. Some treatments can affect fertility. Patients who wish to have children should discuss this with their doctor before treatment begins, when the clinical situation allows.

Possible complications

Complications may result from leukemic cells interfering with normal blood production, the course of the disease, or the effects of treatment. They vary by leukemia type and therapy.

Complications caused by the disease

Anemia – may cause fatigue, weakness, paleness, and shortness of breath.
Thrombocytopenia – increases the risk of bruising and bleeding.
Neutropenia or ineffective white blood cell function – increases the risk of infections, which may be serious.
Accumulation of leukemic cells in organs – may cause enlarged lymph nodes, spleen, or liver and, in some types of leukemia, affect other organs.
Relapse or refractory disease – leukemia may return after a period of remission or may not respond adequately to treatment.

Complications associated with particular types

ALL – leukemic cells may affect the central nervous system.
AML – severe bleeding can occur in its promyelocytic form (APL).
CLL – may be associated with autoimmune hemolytic anemia or immune thrombocytopenia. Rarely, it may transform into an aggressive lymphoma.
CML – without treatment, or if treatment stops working, it may progress to an acute phase.
Leukostasis – in some acute leukemias with very high numbers of leukemic cells, circulation through small blood vessels in the lungs and brain may be impaired. This can cause difficulty breathing, headache, confusion, or blurred vision. It is a medical emergency.

Treatment-related complications

At the start of treatment, rapid destruction of leukemic cells can disrupt the body’s metabolism and damage the kidneys. During treatment, a temporary fall in blood cell counts increases the risk of anemia, infections, and bleeding. Over the longer term, some treatments may affect organ function or fertility and, less commonly, be associated with a second cancer.

Prevention and practical advice

Most cases of leukemia cannot be prevented because their cause is unknown. Some measures may nevertheless help reduce risk or support care during the disease:

Do not smoke, and avoid secondhand smoke.
Avoid exposure to benzene and other harmful chemicals, particularly at work.
Eat a balanced diet and maintain a healthy weight.
Follow your doctor’s advice on preventing infections, especially during treatment.

There is no leukemia screening test recommended for the general population. CHIP is a condition distinct from leukemia, and routine genetic testing for it is not recommended in people without symptoms. If it is discovered incidentally, the doctor assesses whether follow-up blood counts are needed. People at higher risk, such as those who have previously received chemotherapy or radiation therapy, are followed according to their medical history.

When should you consult a doctor?

Consult a doctor if signs or symptoms persist, recur, or worsen, particularly if you experience:

Ongoing fatigue or paleness, shortness of breath, dizziness, or unexplained weakness.
Fever without a clear cause or frequent or recurring infections.
Easy bruising, petechiae, or unusual bleeding.
Swollen lymph nodes, night sweats, unexplained weight loss, or bone pain.
Fullness or discomfort under the ribs, which may be related to an enlarged spleen or liver.

Unexplained changes in a complete blood count, particularly when they persist on repeat tests, should be assessed by a doctor and, when needed, a hematologist.

People with known risk factors may need an assessment or follow-up tailored to their medical history.

If you have been diagnosed with leukemia, contact your hematologist if you develop a temperature of 38°C (100.4°F) or higher, chills, new bleeding or bruising, medication side effects, or new or unusual symptoms.

Frequently asked questions

Is leukemia contagious?
No. Leukemia cannot pass from one person to another, and ordinary contact with someone who has it is safe.

What is the difference between acute and chronic leukemia?
Acute forms involve an accumulation of immature cells and progress quickly. Chronic forms usually develop more slowly and may cause no symptoms at first.

Does treatment always need to begin immediately?
ALL and AML usually require prompt treatment. Some people with CLL who have no symptoms can undergo active monitoring. The hematologist makes the decision according to the subtype and the patient’s condition.

Can leukemia be cured?
The possibility of a cure depends on the type of leukemia, the patient’s age, and the features of the disease. Many children with ALL achieve a long-term cure. In adults with ALL and in AML, the outcome also depends on genetic changes and the response to treatment. CML can often be controlled for many years with targeted therapy, while CLL may remain under control for a long time without disappearing completely.

How long does treatment last?
The duration varies considerably. Initial treatment for acute leukemia may take several weeks, while consolidation or maintenance can extend care over months or years. TKI treatment for CML often continues for years.

Can leukemia return?
Yes. Even during remission, a small number of leukemic cells may remain below the detection level of routine tests. If they begin to multiply again, the disease returns (relapses). “Refractory” means the disease does not respond adequately to treatment. In either situation, the hematologist assesses other treatment options.

Why does early diagnosis matter?

Leukemias are a group of diseases with different courses and treatments. Timely assessment helps identify the subtype, detect complications, and choose appropriate treatment. This is particularly important for acute forms, which may progress quickly. If you have persistent symptoms or unexplained changes in your complete blood count, consult a doctor; these findings can also have other causes.

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📌 Reviewed by Dr. Irma Lapaj, Hematologist, Klinika Kajo.

Leukemia