Leukemia: The Basics

What is Leukemia?

Leukemia is a cancer of the blood or blood cells. There are several types of leukemia and these are classified by how quickly they progress and what cell they affect. In order to understand how leukemia affects the cells, it is helpful to first understand what normal blood cells do.

White blood cells (also called leukocytes) are the body's infection fighting cells.
Red blood cells (also called erythrocytes) give blood its red color, but more importantly, carry oxygen from the lungs to the rest of the body and return carbon dioxide to the lungs as waste.
Platelets (also called thrombocytes) help the body form blood clots to control bleeding.
In addition to these three cell types, the blood also contains fluid called plasma.

All of these products are formed in the bone marrow, a spongy area located in the center of bones. Larger bones have more bone marrow, and therefore produce more cells. The larger bones include the femur (top part of the leg or thigh), the hip bones, and parts of the rib cage. The bone marrow contains a small percentage of cells that are in development and are not yet mature. These cells are called blasts. Once the cell has matured, it moves out of the bone marrow and into the circulating blood. The body has mechanisms to know when more cells are needed and has the ability to produce them in an orderly fashion.

In the case of leukemia, one blood cell goes awry (in the majority of cases this cell is a white blood cell) and the body produces large numbers of this cell. When looked at under a microscope, these abnormally produced cells look different then the healthy cells and do not function properly. The body continues to produce these abnormal, non-functional cells, leaving little space for healthy cells. This imbalance of healthy and unhealthy cells is what causes the symptoms of leukemia.

What Are The Types of Leukemia?

Leukemias are classified by two factors, how quickly the disease develops and what cells are affected. The disease is either classified as acute or chronic, referring to how quickly it develops and progresses. In acute leukemia, the white blood cells multiple very rapidly and are very immature, and therefore cannot function properly (remember, immature cells are called blasts). The blood fills with blasts quickly, causing the patient to develop symptoms and seek medical attention.

In chronic leukemia, the blasts form more slowly, allowing the body to continue to produce functional cells, causing fewer symptoms for the patient. These cases are often diagnosed during a routine physical or blood work. Chronic leukemia may cause the spleen to become enlarged, which can be felt by the doctor during a physical, prompting further investigation.

The types are further divided by the type of white blood cell that is affected, lymphoid cells or myeloid cells. These types are called lymphocytic leukemia and myelogenous leukemia, respectively.

The types include:

Acute myeloid leukemia (also called AML) - occurs in both children and adults.
Acute lymphocytic leukemia (ALL) - the most common type seen in children, but also seen in adults, most often over 65.
Chronic myelogenous leukemia (CML) - occurs mostly in adults, young and old.
Chronic lymphocytic leukemia (CLL) - most often seen in people over age 55, can affect younger adults, but almost never seen in children.

Am I at Risk for Leukemia?

Unfortunately, we do not know what causes leukemia. Several things have been identified as risk factors - that is, exposure to them puts a person at a higher risk of developing leukemia, but it is not a certainty that this exposure will lead to leukemia. These factors include exposure to high-energy radiation, like that released from a nuclear accident or bomb. Some genetic syndromes, such as Down's syndrome, put a person at higher risk. People who work with the chemical benzene over a long period of time also have a greater chance of getting leukemia. Some scientists feel that exposure to electromagnetic fields, like those that come from power lines, may put a person at higher risk, but this has not been proven.

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