Leukemia is a blood cancer originating in the myeloid or lymphoid stem cells, which produce leukocytes (white blood cells) and other cells in the bone marrow. According to the American Cancer Society, lymphocytic leukemia involves overproduction of lymphocytes, while myeloid leukemia involves overproduction of other types of leukocytes, such as monocytes or granulocytes, and sometimes platelets and erythrocytes (red blood cells). Overproduction or one or more blood cells crowds the bone marrow and prevents other types of cells from forming.
Acute vs Chronic
In addition to cell type, leukemia is classified as acute or chronic. Acute leukemia has a fast onset, and immature cells (blasts) are rapidly produced and released into the blood stream. Chronic leukemia develops more slowly, and some cells may appear mature but are often abnormal and don't function properly.
Acute Myeloid Leukemia
Acute myeloid (myelogenous) leukemia is called a variety of names, such as myeloblastic, promyelocytic, monocytic, granulocytic and erythroid, because it arises from the myeloid stem cells that produce all of the blood cells except for lymphoctyes. Chromosomal abnormalities or gene mutations are found with some types of AML. AML is sometimes a secondary cancer caused by chemotherapy.
AML spreads quickly through the blood to other organs, such as the brain, liver and spleen, resulting in fever, infection, anemia, enlarged internal organs, bone marrow pain, weakness, and bleeding. According to the American Cancer Society, AML is most common in adults over 40 (average age 67). While the potential for cure exists, the prognosis is poor for those over 60 with death within a year of diagnosis common.
Chronic Myeloid Leukemia
Chronic myeloid (myelogenous) leukemia is usually related to a specific defect on the Philadelphia chromosome (22). While the bone marrow produces some normal cells, it overproduces immature (blast) cells of various types. CML spreads slowly and may cause few symptoms for years. The American Cancer Society states that cell production eventually expands throughout the bone marrow in the long bones and also in the liver and spleen, causing these organs to enlarge. People begin to feel increasingly tired and short of breath and may experience discomfort as the organs enlarge. Death usually occurs three to five years after diagnosis.
Acute Lymphocytic Leukemia
Acute lymphocytic (lymphoblastic) leukemia derives from uncontrolled overproduction of immature lymphocytes (lymphoblasts) by lymphoid stem cells. The National Cancer Institute reports that lymphocytes comprise B cells, T cells and natural killer cells, all of which are cells that are critical to the immune system. With ALL, these cells don't function properly and production of other necessary cells, such as red blood cells and platelets, falls, resulting in increased infections, anemia, shortness of breath and bleeding. Leukemic cells spread throughout the body causing enlarged liver and spleen and bone pain. The cells may spread to the brain, causing headache and nausea and vomiting. Adult ALL is most common in white males over 70 and is often related to previous chemotherapy or genetic disorders, such as Trisomy 21 (Down syndrome). Prognosis is poor in adults.
Chronic Lymphocytic Leukemia
Chronic lymphocytic leukemia is the most common type of leukemia and, according to the National Cancer Institute, occurs primarily in adults in middle age or later. CLL most often derives from production of abnormal B lymphocytes, which live longer than normal cells but have impaired function. These cells begin to accumulate in the blood. The lymph nodes enlarge as the lymphocytes become trapped. Over time the liver and spleen enlarge, and anemia and bleeding may occur as production of red blood cells and platelets decreases. The impairment in the immune system can result in severe bacterial and viral infections. Survival ranges from eight to 12 years after diagnosis.