Leukemia is a cancer of the blood-forming cells in the bone marrow. Instead of maturing normally, a group of developing white blood cells multiplies out of control, crowding out the healthy cells that carry oxygen, fight infection, and stop bleeding. The fascinating and complex part is that leukemia is not one disease but a family of them, each with its own genetics, behavior, and treatment.
From a specialist’s point of view in haematology, few diseases show so clearly how a single genetic change can reshape the body. Below are the key insights I share with patients and students.
Insight 1: It Starts in the Bone Marrow Factory
The bone marrow is the spongy tissue inside larger bones where all blood cells are made from hematopoietic stem cells. These stem cells give rise to two main branches: the myeloid line (red cells, platelets, and most white cells) and the lymphoid line (lymphocytes). You can read more about this tissue in our article on the composition and function of bone marrow.
Leukemia begins when a cell in one of these lines acquires genetic changes that let it keep dividing without maturing. These abnormal white blood cells accumulate in the marrow and spill into the blood. The result is a paradox: the white count may be very high, yet the person is prone to infection, because the leukemic cells do not function like normal white cells.
Insight 2: There Are Four Main Types
Leukemias are classified by how fast they grow (acute or chronic) and which cell line they come from (myeloid or lymphoid).
| Type | Speed | Who it typically affects | Notable feature |
|---|---|---|---|
| Acute lymphoblastic leukemia (ALL) | Rapid | Mostly children; also adults | The most common childhood cancer |
| Acute myeloid leukemia (AML) | Rapid | Mostly older adults | The most common acute leukemia in adults |
| Chronic lymphocytic leukemia (CLL) | Slow | Older adults | Often found on a routine blood test before any symptoms |
| Chronic myeloid leukemia (CML) | Slow at first | Mostly middle-aged and older adults | Driven by the Philadelphia chromosome (BCR-ABL1) |
Acute leukemias fill the marrow with immature cells called blasts and can make someone seriously ill within weeks. Chronic leukemias involve more mature-looking cells and may progress over years; some people with early CLL are simply monitored for a long time.
Childhood leukemia deserves special mention. Our guides to pediatric acute lymphoblastic leukemia and pediatric leukemia cover how it differs from adult disease.
Insight 3: Genes Tell the Story
For most people, leukemia is not inherited and has no single identifiable cause. It arises from acquired mutations in marrow cells over a lifetime. Some of these changes are now well known and directly shape treatment:
- The Philadelphia chromosome, a swap between chromosomes 9 and 22, creates the BCR-ABL1 fusion gene that drives CML and some cases of ALL.
- FLT3 and NPM1 mutations are common in AML and influence prognosis and drug choice.
- TP53 abnormalities are associated with a more treatment-resistant disease in several leukemia types.
Recognized risk factors include older age, previous chemotherapy or radiation, exposure to benzene, smoking (for AML), certain blood disorders such as myelodysplastic syndromes, and some genetic conditions, notably Down syndrome. Most people who develop leukemia have none of these risk factors.
Leukemia is only one of many conditions a hematologist sees. Inherited disorders such as sickle cell disease behave very differently, and our page of interesting facts about sickle cell anemia makes a useful comparison.
Insight 4: Symptoms Reflect What the Marrow Stops Making
Most signs and symptoms of leukemia make sense once you remember that healthy blood production is being crowded out:
- Too few red cells (anemia): tiredness, breathlessness, pale skin.
- Too few working white cells: frequent or severe infections and fevers.
- Too few platelets: easy bruising, nosebleeds, bleeding gums, tiny red spots on the skin called petechiae.
- Leukemic cells building up: bone pain, swollen lymph nodes, an enlarged spleen, night sweats, and weight loss.
These symptoms overlap with many common illnesses, which is why a simple blood count is often the first real clue.
Insight 5: Diagnosis Is a Layered Process
The path to a diagnosis of leukemia usually begins with a complete blood count and blood film showing abnormal blood results, such as a very high or low white count, anemia, low platelets, or blasts in circulation.
Confirmation normally requires bone marrow biopsy and aspiration, which let a pathologist examine marrow cells directly. In acute myeloid leukemia, finding blasts making up 20% or more of marrow cells has traditionally been the diagnostic threshold, though certain genetic findings allow diagnosis with fewer.
Further tests then refine the diagnosis:
- Flow cytometry identifies which cell line the leukemia comes from by reading proteins on the cell surface.
- Cytogenetics (karyotyping and FISH) looks for chromosome changes.
- Molecular testing, such as PCR and gene sequencing, detects specific mutations.
- Lumbar puncture checks for spread to the spinal fluid, particularly in ALL.
Our guide to leukemia diagnosis tests explains each of these in more depth.
Insight 6: Treatment Is Increasingly Personalized
Treatment depends on the leukemia type, its genetic profile, and the patient’s age and overall health. The main options include:
- Chemotherapy, often given in phases called induction, consolidation and, for ALL, maintenance.
- Targeted therapy, such as tyrosine kinase inhibitors like imatinib for CML, which transformed it from a fatal disease into a condition many people manage with daily tablets.
- Immunotherapy, including antibody treatments and CAR T-cell therapy for some relapsed or resistant leukemias.
- Stem cell transplantation, which replaces the diseased marrow with healthy donor cells and can be curative for some high-risk patients.
One striking example is acute promyelocytic leukemia, a subtype of AML treated with all-trans retinoic acid (a vitamin A derivative) and arsenic trioxide. These drugs push the leukemic cells to mature, and outcomes are now among the best of any leukemia. For an overview of all the types and treatments, see our leukemia guide.
When to See a Doctor
See a doctor promptly if you have persistent tiredness, repeated infections, unexplained bruising or bleeding, fevers or night sweats, or unexplained weight loss lasting more than a couple of weeks. Seek urgent care for heavy bleeding, a high fever with chills, or severe breathlessness. A blood count is quick and inexpensive, and it can rule out or reveal many blood problems.
Frequently Asked Questions
Is leukemia hereditary?
Usually not. Most leukemias arise from genetic changes acquired during life rather than inherited from parents. A small number of families carry inherited predispositions, and a hematologist may suggest testing if several relatives are affected.
Can leukemia be cured?
Many leukemias can be cured or controlled for long periods, especially childhood ALL and acute promyelocytic leukemia. Outcomes depend strongly on the type, the genetic findings, and the person’s age and fitness.
Does a high white blood cell count mean leukemia?
No. Infections, inflammation, stress, smoking and some medicines commonly raise the white count. Leukemia is suspected when the count is extremely high or low, abnormal cells appear on the blood film, or other blood cell lines are also affected.
Why is a bone marrow biopsy needed if blood tests are abnormal?
Blood tests show that something is wrong, but the marrow reveals what the disease is, how much of the marrow it occupies, and its genetic features. Those details decide the exact diagnosis and the best treatment.
