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Questions and answers

What is leukemia?

Leukemia is a disease of the blood-forming system. The short answer is simple, but there is a whole process behind it. Here we explain it calmly, step by step.

Last updated: ~2 min read
Bone marrow, where blood is made
Figure 1.Bone marrow, where blood is made

01Short answer

Leukemia is a cancer of the cells that make blood in the bone marrow. A change in a cell’s DNA stops it maturing normally and makes it multiply out of control. Immature cells build up in the marrow and blood, leaving less room for healthy red cells, white cells and platelets. That causes tiredness, infections and a tendency to bleed. There are several types of leukemia, and treatment depends on the type.

02Simple explanation

Your blood is renewed all the time. The work happens in the bone marrow, the soft tissue inside bones.

In leukemia one blood-forming cell picks up a “faulty” programme and makes many copies of itself. These copies cannot do their job.

As a result there are too few healthy cells: the ones that carry oxygen, fight infection and stop bleeding.

03Scientific explanation

Leukemia is a clonal disease of haematopoietic stem or progenitor cells: somatic genetic changes accumulate in one cell and its descendants gain an advantage.

Which lineage is affected (myeloid or lymphoid) and how fast it behaves (acute or chronic) define the four main types: AML, ALL, CML and CLL.

The diagnosis is made with blood tests, bone marrow examination, flow cytometry and genetic tests.

04What happens in the body?

How blood is made

In the bone marrow, stem cells divide and mature into three main kinds of blood cell: red cells carry oxygen, white cells fight infection and platelets stop bleeding. In a healthy body this is tightly controlled.

What changes in leukemia

A change happens in the genes of one cell. That cell multiplies without maturing and its copies take up space in the marrow, so production of healthy cells falls.

The three main families of blood cells
Figure 2.The three main families of blood cells

What this leads to

Too few red cells cause tiredness and paleness; too few working white cells cause frequent infections; too few platelets cause easy bruising and bleeding. Depending on the type, symptoms develop quickly or slowly.

Immature cells crowd out healthy ones
Figure 3.Immature cells crowd out healthy ones

What matters today

Leukemia is not contagious. Most often the exact cause is unknown, and it is nobody’s fault. Modern treatment helps many people reach remission, and every plan is individual.

05From one cell to a disease

The development of leukemia can be pictured in four simple steps.

The marrow at work — Billions of new blood cells are made every day.1The marrow at workBillions of new blood cells are made every day.
A genetic change — An error appears in one cell’s DNA.2A genetic changeAn error appears in one cell’s DNA.
Uncontrolled growth — The cell copies itself without maturing.3Uncontrolled growthThe cell copies itself without maturing.
Fewer healthy cells — Space in the marrow runs short and symptoms begin.4Fewer healthy cellsSpace in the marrow runs short and symptoms begin.
Understanding helpsKnowing the process makes the doctor’s explanations easier to follow.
Confirm the typeThe type and its genetics shape the treatment plan.

06Key points at a glance

TopicIn brief
How blood is madeIn the bone marrow, stem cells divide and mature into three main kinds of blood cell: red cells carry oxygen, white cells fight infection and platelets stop bleeding. In a healthy body this is tightly controlled.
What changes in leukemiaA change happens in the genes of one cell. That cell multiplies without maturing and its copies take up space in the marrow, so production of healthy cells falls.
What this leads toToo few red cells cause tiredness and paleness; too few working white cells cause frequent infections; too few platelets cause easy bruising and bleeding. Depending on the type, symptoms develop quickly or slowly.
What matters todayLeukemia is not contagious. Most often the exact cause is unknown, and it is nobody’s fault. Modern treatment helps many people reach remission, and every plan is individual.

07Key terms

Bone marrow
Soft tissue inside bones where blood cells are made.
Blast
An immature young blood cell.
Clone
A group of identical cells descended from one cell.

08Key points

  • Leukemia is a cancer of blood-forming cells.
  • It starts in the bone marrow.
  • Symptoms come from a shortage of healthy blood cells.
  • The type and genetics guide treatment.

09Frequently asked questions

Is leukemia a blood disease or a cancer?

Both: it is a cancer of blood-forming cells.

Can I protect myself against it?

Most often the exact cause is unknown, so there is no specific protection.

Does leukemia behave the same in everyone?

No. Type, age, genetics and response to treatment change the course a great deal.

10Questions for your doctor

Take these questions to your appointment. The ones you save are collected on the “My questions” page and stay on this device only.

  1. Is leukemia a blood disease or a cancer?

  2. Can I protect myself against it?

  3. Does leukemia behave the same in everyone?

My questions

12Sources

  1. National Cancer Institute (NCI). Leukemia—Patient Version
  2. MedlinePlus (U.S. National Library of Medicine). Leukemia
  3. National Cancer Institute (NCI). What Is Cancer?
  4. NHS. Acute myeloid leukaemia
  5. National Cancer Institute (NCI). Common Cancer Myths and Misconceptions
  6. NHS (UK). Acute lymphoblastic leukaemia
  7. NHS (UK). Chronic lymphocytic leukaemia
  8. NHS (UK). Chronic myeloid leukaemia
  9. American Cancer Society. Risk Factors for Acute Myeloid Leukemia (AML)
  10. Cancer.Net (ASCO). Talking With Family and Friends
Medical disclaimerThis information is for educational purposes only and does not replace medical advice.
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