Leukemia is a cancer of the blood and bone marrow. In simple terms, cancer is defined as the uncontrolled growth of abnormal cells. Cancer can develop anywhere in the body. In leukemia, this rapid, out-of-control growth of abnormal cells takes place in the bone marrow of bones. These abnormal cells then spill into the bloodstream. Unlike other cancers, leukemia generally doesn’t form into a mass (tumor) that can be seen in imaging tests, such as X-rays.

Leukemia begins in the developing blood cells in the bone marrow. All blood cells start out as hematopoietic (hemo = blood; poiesis = make) stem cells. The stem cells undergo multiple stages of development until they reach their adult form.

First, blood stem cells develop into either myeloid cells or lymphoid cells. If blood cells were to continue to develop completely normally, the adult forms of these cells are as follows:

Myeloid cells develop into red blood cells, platelets, and certain types of white blood cells (basophils, eosinophils and neutrophils).

Lymphoid cells develop into certain types of white blood cells (lymphocytes and natural killer cells).

So inside the bone marrow, blood cells are beginning to multiply and divide into red blood cells, white blood cells and platelets. However, if you have leukemia, one of these blood cell types begins to rapidly multiply, in an out-of-control manner. These abnormal cells – called leukemia cells – begin to take over the space inside the bone marrow. They crowd out the other normal cell types that are trying to develop. This is bad in a number of ways:

Unlike other blood cell types, the leukemia cells are abnormal and serve no useful purpose.

The other cell types (red blood cells, white blood cells and platelets) have very little space and support to continue to grow and multiply inside the bone marrow.

This results in fewer normal blood cells being made and released into the blood and more leukemia cells being made and released into the blood. Without an adequate amount of normal blood cells, your body’s organs and tissues will not get the oxygen they need to work properly, your body won’t be able to fight off infection or clot blood when needed.

Acute leukemia. The leukemia cells are rapidly dividing and the disease progresses quickly. If you have an acute leukemia, you would feel sick within weeks of the leukemia cells forming. Acute leukemia is the most common pediatric cancer.

Chronic leukemia. Often, these leukemia cells have features of both immature and mature cells. Some of these cells may have developed to the point where they do function as the cells they were meant to become, but not to the extent their normal counterparts do. The disease typically worsens slowly as compared to acute leukemia. If you have chronic leukemia, you may not have noticeable symptoms for years. Chronic leukemia is more commonly seen in adults as compared to children.

Myelogenous or myeloid leukemia means the leukemia has developed from the myeloid cell line. Normal myeloid cells develop into red blood cells, white blood cells and platelets.

Lymphocytic leukemia means the leukemia has developed from the lymphoid cell line. Normal lymphoid cells develop into white blood cells that are an important part of the body’s immune system.

Editorial Team
Journal of Cancer Epidemiology and Prevention
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