1.+Introduction



Leukemia is a cancer of the blood or bone marrow. Leukemia is characterized by an abnormal increase of white blood cells in the blood-stream.Leukemia is a type of //lymphoma//, a cancer that affects the lymphatic system.



Leukemia occurs when the cells of the bone marrow, (known //as hematopoietic tissue//) begin multiplying uncontrollably and produce large amounts of white blood cells (known as //lymphocytes//). Because the white blood cells multiply out of control and are a drain on resources, they are cancerous. The lymphocytes produced during leukemia are abnormal - they are immature and cannot perform their functions properly.

There are four main types of leukemia: **acute lymphoblastic leukemia**, **chronic lymphocytic leukemia**, **acute myelogenous leukemia**, and **chronic myelogenous leukemia**. Of these types, the latter three infect adults (ages 20+) almost exclusively, with less than 5% of diagnosed cases being children. Acute lymphoblastic leukemia only affects children.



In **acute leukemia**, a large number of severely immature and abnormal lymphocytes(known as blastocytes) are produced at a rapid and tremendous rate by the bone marrow. Acute leukemia spreads incredibly quickly, and requires rapid hospitalization and treatment.

In **chronic leukemia**, the affected bone marrow produces various types of immature white blood cells (not just lymphocytes) at a rate that is slower than acute leukemia, but still abnormally fast. Treatment is often delayed until the disease has progressed sufficiently, in order to kill as many immature cells as possible.

Lymphoblastic/lymphocytic cancer affects the //yellow marrow//, where B-cell lymphocytes are produced and mature. Myelogenous cancer affects the //red marrow//, where other types of blood cells are made.

Leukemia is an especially virulent cancer. Because the abnormal white blood cells travel through the lymphatic system - an extensive network of vessels that carry lymph around the body - malignant leukemia can quickly spread to ALL parts of the body through metastasis** if not treated quickly - making the survival rate of metastized, advanced leukemia extremely low.