What is Leukemia?- The Leukemia and Lymphoma Society

Leukemia is a malignant disease (cancer) of the bone marrow and blood.
It is characterized by the uncontrolled accumulation of blood cells.
Leukemia is divided into four categories: myelogenous or lymphocytic,
each of which can be acute or chronic. The terms myelogenous or lymphocytic
denote the cell type involved. The are four major types of leukemia.

Leukemia is the general term used to describe four different
disease-types called:

* Acute Myelogenous Leukemia (AML)
* Acute Lymphocytic Leukemia (ALL)
* Chronic Myelogenous Leukemia (CML)
* Chronic Lymphocytic Leukemia (CLL)

The terms lymphocytic or lymphoblastic indicate that the cancerous change takes place in a type of marrow cell that forms lymphocytes. The terms myelogenous or myeloid indicate that the cell change takes place in a type of marrow cell that normally goes on to form red cells, some types of white cells, and platelets.

Acute lymphocytic leukemia and acute myelogenous leukemia are each composed of blast cells, known as lymphoblasts or myeloblasts. Acute leukemias progress rapidly without treatment.

Chronic leukemias have few or no blast cells. Chronic lymphocytic leukemia and chronic myelogenous leukemia usually progress slowly compared to
acute leukemias.

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How does leukemia develop?

The four types of leukemia each begin in a cell in the bone marrow. The cell undergoes a leukemic change and it multiplies into many cells.
The leukemia cells grow and survive better than normal cells and, over time,
they crowd out normal cells.

Normal stem cells in the marrow form three main cell-types: Red cells, platelets and white cells. There are two major types of white cells: germ-ingesting cells (neutrophils and monocytes) and lymphocytes, which are part of the body's immune system and help to fight to infection.

The rate at which leukemia progresses and how the cells replace the normal blood and marrow cells are different with each type of leukemia.

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