What is Leukemia?
Leukemia is cancer of the blood forming tissues of the body, including bone marrow and the lymphatic system. Leukemia usually begins in the white blood cells and typically manifests when bone marrow produces a large number of abnormal white blood cells that don't function properly.

To put is another way, a person with leukemia has a body that makes abnormal white blood cells. Unlike normal blood cells, leukemia cells don't die when they should. These abnormal cells may crowd out normal white blood cells, red blood cells, and platelets making it hard for the normal, healthy blood cells to do their work.

Types of leukemia
Leukemia isn't just a children's disease. This type of cancer is classified by four main types and many subtypes - and only some are common among children. Types of leukemia can be grouped based on how quickly the disease develops and gets worse. Doctors classify leukemia in two primary ways:

1. How fast leukemia progresses
2. Type of white blood cell affected

Progression

Acute leukemia - Acute leukemia progresses quickly. During acute leukemia, abnormal blood cells called "immature blasts can't carry out the normal work of blood cells and multiply rapidly so that the disease worsens quickly. Acute leukemia requires aggressive, timely treatment.

Chronic leukemia - Chronic leukemia progresses slowly. This type of leukemia involves more mature blood cells that can still do some of the work of normal white blood cells. These blood cells replicate or accumulate more slowly and can function normally for a period of time.

Type of white blood cell affected

Lymphocytic leukemia - This type of leukemia affects the lymphoid cells or lymphocytes, which form lymphoid or lymphatic tissue. Lymphatic tissue is the main component of the immune system and is found in various places throughout the body, including the lymph nodes, spleen and tonsils.

Myelogenous leukemia - This type of leukemia affects the myeloid cells which include cells that later develop into red blood cells, white blood cells and platelet-producing cells.

There are also four common types of leukemia:

1.  
   1. Chronic lymphocytic leukemia (CLL) - During CLL, a common adult leukemia, people may feel well for years without treatment. Most often, people diagnosed with the disease are over age 55. It almost never affects children. 
   2. Chronic myeloid leukemia (CML) - This type of leukemia mainly affects adults and is associated with a chromosome abnormality called the Philadelphia chromosome.
   3. Acute lymphocytic (lymphoblastic) leukemia (ALL) - ALL is the most common type of leukemia in young children but can also affect adults. 
   4. Acute myeloid leukemia (AML) - AML affects myeloid cells and grows quickly, occuring in both adults and children. This is the most common type of leukemia.

Leukemia can affect both adults and children. But who is most at risk of developing leukemia? And how can risk factors be avoided? Continue reading for more information on which populations are at risk of the disease and what can cause leukemia.  Facts about leukemia here.