What is Leukemia?

Leukemia is a cancer of the blood cells. There are various types of blood cells, red blood cells to carry oxygen and white blood cells to fight infections. Also, another type of blood cell called "platelets" are fragments which assist in clotting. Amazingly, all of the various types of blood cells originate from a single type of cell, called the "pleuripotential cell", which resides in the bone marrow. Some blood cells (like the pleuripotential time) stay inside the bone marrow, while the more mature types (like red and white blood cells) are meant to circulate through the bloodstream, to go to wherever they are needed. Leukemia is usually a cancer of the white blood cells. It is divided into type general types, Acute and Chronic. This distinction is based upon their untreated behavior-- with no treatment acute leukemias will kill within months, while chronic leukemia patients may live for many years. However, there is a flipside to this--it is usually easier to cure acute leukemia than the chronic variety. Both acute and chronic leukemias are further subclassified as to the particular type of blood cell they arise from. White blood cells are larger than red blood cells and are easy to see under the microscope. Too few white blood cells ("leucopenia") leads to massive infections, with bacteria, viruses and fungi. Too few red blood cells leads to anemia, with pallor and weakness. Too few platelets lead to easy bruising and internal bleeding. Acute leukemias, unlike the chronic variety, often have normal or decreased white blood cells. A hallmark of all leukemias is insufficient production of other normal blood cells, since the resources are being diverted to the leukemic cell population (also called the "leukemic clone"). This will be seen when we look at the symptoms of leukemia.

Another crucial distinction in leukemias besides "acute" and "chronic" is between the Lymphocytic and Myelogenous types. The Lymphocytic variety comes from lymphocytes, which is a common white blood cell active in identifying and marking germs to be killed. In adults, about 1/3 of the total white blood cells are lymphocytes, and in young children up to 2/3 are lymphocytes. The Myelogenous variety comes from other blood cells besides lymphocytes, represents at least 7 different subtypes, and is often just called"non-lymphocytic" leukemia. These non-lymphocytic types may arise from the red blood cell line ("erythroleukemias") or from the platelet line ("megakaryocytic types"). Sometimes the types are found in combination, that is the disease is composed of more than one type of leukemia. Also, as the disease gets more advanced, it may start showing other "clones" instead of the "pure type" that it started as. The major divisions of acute and chronic, and lymphocytic and myelogenous, are combined into the following four labels into which all leukemia’s can be grouped:

ALL (Acute Lymphocytic Leukemia)

AML (Acute Myelocytic Leukemia)

CLL (Chronic Lymphocytic Leukemia)

CML (Chronic Myelogenous Leukemia)

Sometimes a previous chronic leukemia will convert into the acute variety (called "Richter's syndrome") but since the clinical behavior and treatment of the acute and chronic types are different, they are considered as two separate topics. Like all cancers, leukemia starts from a single abnormal cell, and the type of cell will determine the type of leukemia. A change occurs in the genes of this cell, that is in the information stored in the cells "DNA". Each body cell contains the information necessary to form a whole new body, but most of this is "masked" after the cell develops ("differentiates") into a particular adult cell type. The genes can be altered to command the cell to undergo uncontrolled division, and this is then cancer. Ultimately, cancer is a disease of the DNA! Different recognized genetic abnormalities are found in the various subtypes of leukemia, this is an area of active research. Anyway, the abnormal cell makes billions of copies of itself, shunting resources away from normal cells division. The "leukemic clone" takes over the bloodstream, choking off normal functioning and leading to the symptoms described below. If untreated, acute leukemia is always fatal.

How Common is Acute Leukemia?

Combining childhood and adult cases, there totals 11,000 new cases per year in the U.S.A. Acute leukemia is the most common cancer of childhood. However, only 25% of the total cases occur in children. Overall, acute leukemia strikes 5 out of 100,000 people each year.AML is 5 times more common than ALL but ALL