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.
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.
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:
Unfortunately, we do not know what causes most cases of 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. Prior treatment with certain types of chemotherapy and having a personal history of certain blood disorders such as myelodyplastic syndrome (MDS), are also risk factors. Finally, smoking cigarettes increases the risk of acute myelogenous leukemia because it is a source of exposure to benzene. It is important to realize that many patients with leukemia do not have any identifiable risk factors.
Because we do not know the exact cause, it is not possible to recommend ways to prevent leukemia. If possible, one should avoid smoking, exposure to radiation, and the chemical benzene.
Leukemia is not a cancer that we screen for because it is rather rare (accounting for 3% of all new cancer cases), and early detection does not improve survival in most cases. To determine if a person has leukemia, a blood count would be drawn by the doctor, which would show an abnormally low or high number of white blood cells in a person with the disease. Regular physicals by your healthcare provider are your best method of screening.
The blast cells are unable to perform their normal function of fighting infection, so patients may develop fevers or infections that won't go away. As the number of immature cells (blasts) increases, the normal cells are crowded out. This leads to low red blood cell counts and low platelet counts. A low red cell count is called anemia, which may cause the patient to feel tired or appear pale. A low platelet count affects blood clotting, causing the patient to bleed or bruise easily.
As mentioned before, acute leukemia tends to cause symptoms more rapidly than chronic leukemia. These patients tend to go to their healthcare provider because they feel sick. In chronic leukemia, symptoms may not appear for some time, and when they first appear, they may be mild. These cases are often found during a routine physical.
Some common symptoms include: fever, chills, weakness and fatigue, swollen or tender lymph nodes, liver or spleen, easy bleeding or bruising, swollen or bleeding gums, night sweats, weight loss, and bone or joint pain. In acute leukemia, the abnormal cells can accumulate in the brain or spinal cord, causing headaches, vomiting, confusion, or seizures.
In both acute and chronic leukemia, the healthcare provider asks about medical history and conducts a physical exam. During the exam, abnormalities such as enlarged spleen, liver or lymph nodes may be detected, prompting further investigation. A laboratory test called a complete blood count would find blast cells present in the blood, thus suggesting a diagnosis of leukemia. This test can reveal that the patient has leukemia, but further testing is required to determine the type.
To determine the type of leukemia, the healthcare provider takes a sample of the bone marrow. This is done by inserting a needle into a bone (usually the hip bone) and removing a sample of the marrow. These cells are examined under a microscope, allowing the physician to determine what cell is abnormal, and whether it is an acute or chronic leukemia. It may also be necessary to perform a lumbar puncture (spinal tap) to determine if leukemia cells have entered the nervous system. This decision is dependent on the type of leukemia and the patient's symptoms.
Treatment is dependent on the type of leukemia, and may differ dependent on the patient's age, health and extent of the disease. For specific treatments, look below for links to the National Cancer Institute's PDQ.
Leukemia is a complex disease, and with about 54,270 cases per year in the United States, it is relatively rare. The disease is slightly more common in males and is also more common in Caucasians than African-Americans. Due to the relative rarity of the disease, it is recommended that patients receive treatment at a medical center that is experienced in treating the disease. Acute leukemias need to be treated quickly. The goal of therapy is to induce a remission, which means there is no evidence of leukemic cells, and the body returns to normal. Once this is achieved, patients often receive further therapy to prevent a relapse (return of the disease), which is called consolidation therapy.
Chronic leukemias may not need to be treated right away, depending on the symptoms at diagnosis. It has been thought in the past that chronic leukemias could never be cured, but this thinking has changed with the development of new therapies.
Patients with acute leukemia are followed closely, with frequent monitoring of blood cell counts, to watch for relapse, after therapy has induced a remission. Patients who have a remission that lasts five years are generally considered cured. In chronic leukemia, blood counts may be monitored for years, with or without treatment, depending on the case.
There have been many promising advances in the treatment of leukemia over the past 40 years. In 1960, only 14% of all patients with leukemia were alive five years after diagnosis. This number increased to 35% in 1970, and is now about 46%. The death rate of children with all types of leukemia has decreased by 61% since the 1970s. Survival of children with acute lymphocytic leukemia, specifically, has increased from 53% to 82% during the same time period. These advances have been made possible by researchers dedicated to studying leukemia and clinical trials of innovative leukemia therapies.
Niederhuber, J. E., Armitage, J. O., Doroshow, J. H., Kastan, M. B., Tepper, J. E., & Abeloff, M. D. (2014). Abeloff's clinical oncology, 5th edition (2186 p.).
The American Cancer Society. Facts and Figures 2015. www.cancer.org
National Cancer Institute
The Leukemia & Lymphoma Society
U.S. Cancer Statistics Working Group. United States Cancer Statistics: 1999–2007 Incidence and Mortality Web-based Report. Atlanta (GA): Department of Health and Human Services, Centers for Disease Control and Prevention, and National Cancer Institute; 2010. Available at: www.cdc.gov/uscs
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