What Is Leukemia?

Where does leukemia actually start? Not in a lump you can feel, in most cases — it starts in the bone marrow, the soft tissue inside your bones where blood cells are made. When that factory goes wrong, it can pour out large numbers of abnormal white blood cells that do not work properly, and leave too little room for the healthy cells you need.

What goes wrong in the marrow?

Healthy marrow makes a balanced mix: red cells to carry oxygen, platelets to help blood clot, and white cells to fight infection. In leukemia, a change in a developing white cell causes it to multiply out of control. Those abnormal cells build up in the marrow and spill into the bloodstream, crowding out normal production.

The animation at the top of this page, "Acute Myeloid Leukemia AML" (about two and three-quarter minutes), illustrates exactly that process for one type — how AML develops in the blood and bone marrow — and goes on to discuss symptoms and treatment options. It is a useful visual starting point because leukemia is, at its core, a problem of cell production rather than a single tumour.

As healthy cells fall, the effects make sense: too few red cells can leave you tired and pale, too few platelets can mean bruising or bleeding more easily, and white cells that do not function well can mean infections that keep coming back. Not everyone has all of these, and they develop at very different speeds depending on the type.

Aren't there several different leukemias?

Yes — and that is why two people with "leukemia" can have quite different experiences. Doctors group leukemias first by how fast they develop — acute, meaning faster-growing, or chronic, meaning slower — and then by the family of white cells involved, mainly myeloid or lymphoid. That gives four main combinations you will hear named, including acute myeloid leukemia (AML) and chronic myeloid leukemia (CML).

A second video on this site, "chronic myelogenous leukemia" (about three and a half minutes), looks at the chronic myeloid form, describing it as a disorder in which one family of white cells — the granulocytic line — proliferates more than it should. Watching the two videos together gives a fair sense of the range: one acute and fast-moving, one chronic and slower.

How do doctors confirm it?

It usually starts with blood tests. A full blood count can show abnormal numbers or immature cells that should not normally be circulating, and the blood can be examined under a microscope. To confirm the diagnosis and identify the exact type, doctors typically need a sample of bone marrow as well, along with laboratory tests that characterise the abnormal cells. That typing step matters — treatment is chosen for the specific leukemia, not for the word alone.

If blood conditions more broadly are what brought you here, our guide to what anemia is explains the low-red-cell side of the picture, and for some leukemias a transplant is part of the conversation — see what a bone marrow transplant involves.

What does treatment generally involve?

Treatment depends on the type, how fast it is moving, and the person's overall health, and it is planned by a specialist team. Approaches commonly include chemotherapy medicines, targeted medicines for certain types, and in selected cases a stem cell or bone marrow transplant. Chronic types are sometimes monitored or controlled with ongoing targeted treatment rather than treated intensively straight away. Your own team is the right source for what applies in an individual case — this article can explain the landscape, but it cannot map your route through it.

Frequently Asked Questions

Is leukemia contagious?

No. Leukemia is not an infection and cannot be passed from person to person. It develops from changes in a person's own blood-forming cells.

Can leukemia be found on a routine blood test?

Sometimes the first clue does appear on a routine blood count, when cell numbers look abnormal. A blood test alone is not the whole diagnosis, though — confirming leukemia and its type usually needs further laboratory tests and a bone marrow sample.

Does everyone with leukemia need a bone marrow transplant?

No. Transplants are used only for selected types and situations. Many people are treated with chemotherapy or targeted medicines, and some chronic leukemias are managed with ongoing treatment and monitoring.

MedicalVideos.com has published trusted medical videos since 2007. The site was founded by Dr. Mohamed Ibrahim, MD, PhD — physician-scientist.

Educational only — this article is general information about leukemia, not medical advice and not a diagnosis. Persistent tiredness, repeated infections, or unexplained bruising or bleeding should be discussed promptly with a clinician.