Leukemia is a cancer of the bone marrow and blood (usually involving the white blood cells). White blood cells give your body the power to fight infection and stay healthy, but in people who develop leukemia, the bone marrow rapidly produces an uncontrollable amount of abnormal white blood cells that fail to function properly. These cancerous cells begin to take over the space inside the marrow and crowd out the healthy blood cells.

This results in fewer normal blood cells (and more abnormal leukemia cells) being produced and released into the blood. Without enough normal blood cells, the body’s organs and tissues do not get adequate oxygen, and the body isn’t able to ward off infection or clot blood when needed.

Types of Leukemia

The four main types of leukemia are named for the cell type affected—myeloid or lymphoid—and how quickly the leukemia grows. Chronic leukemia refers to a disease where the cancerous cells are more mature and grow slowly, while acute leukemia is characterized by less developed cells that multiply rapidly and require aggressive treatment.

Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is the most common type of acute leukemia in adults. It also has numerous subtypes, and the specific type you are diagnosed with will determine which treatment is recommended.

AML is a fast-growing cancer that develops from myeloid cells, which can produce white blood cells, red blood cells, and platelets. Abnormal changes in these cells prevent them from becoming mature and being able to protect the body. As they multiply, they quickly overwhelm the normal cells in the bone marrow and blood.

Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is the most common type of chronic leukemia in adults. CLL is a cancer of B-cells, which are lymphocytes (a type of white blood cell) that make antibodies to fight germs.

CLL is usually a slow-growing cancer, but over time, it results in too many abnormal B-cells that crowd out healthy cells in the bone marrow.

Chronic Myeloid Leukemia

Chronic myeloid leukemia (CML) is a rare, slow-growing cancer that occurs most often in adults over the age of 65. In CML, too many granulocytes (a type of white blood cell) are present in the body.

CML is different from the other types of leukemia in that it is strongly connected with an abnormal chromosome called the Philadelphia (Ph) chromosome. This occurs when a piece of chromosome 22 breaks off and attaches to chromosome 9, or vice versa. The breaks in both chromosomes result in an abnormal fusion gene that leads to uncontrolled cell growth.

Acute Lymphocytic Leukemia

Acute lymphocytic (or lymphoblastic) leukemia (ALL) occurs more often in children. ALL is a cancer that involves abnormal B-cells or T-cells, which are types of lymphocytes that work together to attack germs and diseased cells.

Other rarer types of leukemia and pre-leukemic conditions also exist, including:

• Hairy cell leukemia: This disease is a rare, slow-growing cancer of the blood in which the bone marrow makes too many B-cells (lymphocytes). These excess B-cells are abnormal and look “hairy” under a microscope.
• Myelodysplastic syndromes: This group of disorders is caused by poorly formed blood cells or ones that don't work correctly and often result from a problem in the bone marrow. In some cases, individuals with MDS may develop acute leukemia.
• Myeloproliferative disorders: These disorders can affect various types of blood cells and can eventually cause individuals to develop acute leukemia.

Leukemia Symptoms

Symptoms of leukemia are often vague and may feel similar to the symptoms of other common illnesses.

The most common symptoms include:

• Persistent fatigue, weakness, or a lack of energy
• Tiny red or purple spots on the skin
• A pale skin tone
• Fever or chills
• Recurrent nosebleeds
• Bleeding and bruising easily
• Unexplained weight loss
• Joint or bone pain
• Swollen lymph nodes
• Frequent infections
• Shortness of breath

Risk Factors: What Causes Leukemia?

Researchers haven’t yet identified the exact reason why many types of leukemia occur. However, certain genetic and environmental factors may raise your risk of developing leukemia, including:

• Having undergone previous chemotherapy or radiation therapy
• Certain genetic disorders (such as Down syndrome)
• Exposure to certain chemicals found in gasoline and used in industrial settings (such as benzene)
• Having a smoking history
• Having a family history of the disease
• Being age 65 or older
• Being male
• Being Caucasian

Having any of these risk factors does not mean you will develop leukemia, and many people with leukemia have no risk factors at all. However, if you are experiencing any of the symptoms listed above, you should contact your doctor.