Acute Lymphocytic Leukemia - Introduction

Introduction

The word leukemia literally means "white blood" and is used to describe a variety of cancers that begin in the blood-forming cells (lymphocytes) of the bone marrow.

Leukemias are divided into two major types:

• Acute (which progresses quickly with many immature white cells)
• Chronic (which progresses more slowly and has more mature white cells)

Both leukemia and lymphomas (Hodgkin’s disease and non-Hodgkin’s lymphomas) are cancers of lymphocytes. The difference is that leukemia starts in the bone marrow while lymphomas originate in lymph nodes and then spread to the bone marrow or other organs.

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White blood cells (leukocytes) evolve from immature cells referred to as blasts. Malignancy of these blast cells is the source of leukemias, which generally progress as follows:

• Normally, blasts constitute 5% or less of healthy bone marrow. In leukemia, however, these blasts remain immature and multiply continuously, eventually constituting between 30 - 100% of the bone marrow.
• Eventually these malignant blast cells fill up the bone marrow and prevent production of healthy red cells, platelets, and mature white cells (leukocytes).

Malignant blasts spill out of the marrow into the bloodstream and lymph system and can travel to the brain and spinal cord (the central nervous system). Some blasts are called lymphoblasts (which become mature cells called lymphocytes) and others are called myeloblasts (which mature to myeloid cells).

Acute leukemias subdivided into two classifications according to whether the malignant blasts are lymphocytes or myeloid:

• Acute lymphocytic leukemia (ALL), which is the subject of this report
• Acute myeloid leukemia (AML), which is not covered in this report

Acute Lymphocytic Leukemia

Acute lymphocytic leukemia (ALL) is also known as acute lymphoid leukemia or acute lymphoblastic leukemia. The majority of childhood leukemias are of the ALL type.

Lymphoctyes are the body’s primary infection fighters. Among other vital functions, lymphocytes produce antibodies, factors that can target and attack specific foreign substances (antigens).

Lymphocytes develop in the thymus gland or bone marrow and are therefore categorized as either B cells (bone marrow-derived cells) or T cells (thymus gland-derived cells).Malignancies in ALL can arise either in T-cell or B-cell lymphocytes. Most cases of ALL involve B-cell types.

Review Date: 01/27/2011
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org).