Types of Leukemia

(via Mayo Clinic)

Doctors classify leukemia in two ways.

Speed of progression
The first type of classification is by how fast the leukemia progresses:

• Acute leukemia. In acute leukemia, the abnormal blood cells are immature blood cells (blasts). They can't carry out their normal work, and they multiply rapidly, so the disease worsens quickly. Acute leukemia requires aggressive, timely treatment.
• Chronic leukemia. This type of leukemia involves more mature blood cells. These blood cells replicate or accumulate more slowly and can function normally for a period of time. Some forms of chronic leukemia initially produce no symptoms and can go unnoticed or undiagnosed for years.

Types of cells affected
The second type of classification is by type of white blood cell affected:

• Lymphocytic leukemia. This type of leukemia affects the lymphoid cells or lymphocytes, which form lymphoid or lymphatic tissue. This tissue is the main component of the immune system and is found in various places throughout your body, including your lymph nodes, spleen and tonsils.
  
• Myelogenous (MI-uh-loj-uh-nus) leukemia. This type of leukemia affects the myeloid cells. The myeloid cell line includes cells that later develop into red blood cells, white blood cells and platelet-producing cells.

Major types
The major types of leukemia are:

• Acute myelogenous leukemia (AML). This is the most common type of leukemia. It occurs in children and adults. It's also called acute nonlymphocytic leukemia.
• Acute lymphocytic leukemia (ALL). This is the most common type of leukemia in young children. ALL accounts for about 75 percent of all childhood leukemias.
• Chronic lymphocytic leukemia (CLL). With CLL, a common adult leukemia, you may feel well for years without treatment. CLL is more common in Jewish people of Russian or Eastern European descent. It almost never affects children.
• Chronic myelogenous leukemia (CML). This type of leukemia mainly affects adults. It's associated with a chromosome abnormality called the Philadelphia chromosome, which creates an abnormal gene called BCR-ABL. The BCR-ABL gene produces an abnormal protein called tyrosine kinase that doctors and researchers believe causes leukemia cells to grow and develop. A person with CML may have few or no symptoms for months or years before entering a phase in which the leukemia cells grow more quickly.
• Other chronic myeloid disorders. Like CML, this group of diseases causes chronic leukemia by the creation of too few or too many myeloid cells. Chronic myeloid disorders include myelodysplastic syndromes and myeloproliferative disorders, such as essential thrombocythemia, polycythemia vera and myelofibrosis. These conditions may lead to acute myeloid leukemia.

Other, rarer types of leukemia include hairy cell leukemia and chronic myelomonocytic leukemia.