A Brief Overview

Leukemia is a cancer of the blood, affecting the production of healthy white blood cells.  Cancerous cells found in the bone marrow divide abnormally, producing huge numbers of immature immune cells.  These cells are produced in such high numbers that they crowd the marrow space, blocking the production of healthy immune cells and eventually spilling into the blood stream, traveling to other organs in the body and causing damage.

Think of it as a tree.  A single stem cell exists as the base of the trunk.  That cell dividing and differentiating is like traveling up the trunk and reaching the branches.  Here there can be thousands of cells, like the leaves, but each could have a different function.  Like a tree, these cells all grew up from the trunk and branched into different specialities.  Leukemia affects this tree by causing a single branch on it to grow uncontrollably, causing so much disproportion that the tree as a whole cannot survive.  Many different types of leukemia exist and are classified based on what cell types the cancer affect.  The four most common types are Lymphoblastic Leukemia and Myelogenous Leukemia, both of which can occur acutely or chronically.  These two titles refer to the specific cell lineage found to be cancerous (lymphoid or myeloid white blood cells).  In these forms, the cancer can be though of as occurring near the ends of the branch, that is, once the cell lines have become relatively differentiated.

Leukemia affects people of all ages, genders, and races.  Approximately 45,000 people will be diagnosed with leukemia in the United States in 2009.  It has a higher prevalence among the elderly (median age at diagnosis is 66), men (57%), and individuals of European descent (12.8 per 100,000).  Leukemia is the most common form of cancer in children (33% of total cancer diagnoses in children <14 years old).  The overall five year survival rate among the four major leukemias among all ages is 55%, but it should be noted that children have a significantly higher survival rate than the entire population.

Statistics taken from the Leukemia and Lymphoma Society.