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White blood cells play the important role of protecting the body against foreign invaders by their ability to act as immune cells. They can be called into play on a moment’s notice to help keep a virus or bacteria from gaining a foothold and causing illness. On the other hand, in a group of cancers called leukemia, white blood cell production spirals dangerously out of control. What is the pathophysiology of leukemia?
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Types of Leukemia
All leukemias have one thing in common, they all involve the uncontrolled production of white blood cells that are abnormal in appearance and function.
Leukemia is classified into types based on the kind of white blood cell affected and whether the increase in white blood cells occurs quickly or slowly. When there’s a rapid increase in abnormal white blood cells and the cells are very immature, it’s called an acute leukemia. When abnormal white blood cell production proceeds more slowly and the cells more closely resemble mature white blood cells, the leukemia is classified as chronic.
Leukemia is also divided into classes based on the type of abnormal white blood cell produced. When the abnormal cells would normally have gone on to become lymphocytes, it’s called a lymphocytic or lymphoblastic leukemia, depending upon how mature the cells are. If the abnormal cells were destined to become red blood cells, platelets or other types of white blood cells, it’s classified as a myelogenous or myeloblastic leukemia. Thus, there are acute and chronic myelogenous leukemias and acute and chronic lymphocytic leukemias. There are also other subtypes of leukemia that are less common.
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Leukemia All Starts with a Mutation
The pathophysiology of leukemia isn’t completely understood, but the initiating event is likely a mutation in the genetic material called DNA that’s present in the cells in the bone marrow. When this mutation occurs, it alters other genes that help to keep cancer in check.
A variety of environmental exposures increase the risk of mutations that damage DNA including exposure to ionizing radiation, toxins and certain chemicals. In addition, some people are genetically predisposed to leukemia and are more likely to develop leukemia when one of these mutations occurs. Some experts believe that certain types of viruses, particularly retroviruses, are involved in certain types of leukemia.
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What Happens After the Mutation?
Once a mutation or mutations in DNA occurs that can’t be repaired, the abnormal white blood cells can freely replicate and become essentially “immortal". These abnormal white blood cells no longer function normally, yet they continue to freely replicate. When they do, they start to crowd out blood cells that do function normally. This increases the risk of infections – one of the most common causes of death in people with leukemia. This overabundance of abnormal white blood cells also reduces the number of red blood cells and platelets, leading to anemia and bleeding problems.
Leukemic cells can also invade other tissues such as the spleen, liver, lymph nodes and bone and cause tissue destruction. The abnormal cells are dividing rapidly, and they selfishly use the resources of other cells to reap their deadly destruction.
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The Bottom Line
The pathophysiology of leukemia is complex, but, in summary, the rapidly dividing, abnormal white blood cells take over by utilizing the resources of normal tissues and cells. If untreated, this eventually leads to death.
Fortunately, there are treatments that keep leukemic cells under control, so that in many cases, a person with leukemia can lead a fairly normal existence. The treatments for leukemia have improved over the years, which is good news for anyone who receives this unwelcome diagnosis.
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Merck Manual. Eighteenth edition. 2006.
Emedicine. "Acute Lymphoblastic Leukemia"
Emedicine. "Chronic Lymphocytic Leukemia"