Leukemia refers to cancers of the white blood cells.

Normal white blood cells, called leukocytes, play a central role in fighting infections.

They have a very short life span (sometimes only a few hours) and are continuously replenished in the bone marrow.

In leukemia, the bone marrow creates abnormal white blood cells that don’t mature properly, cannot fight infection effectively, and don’t die like normal cells.

Instead, they build up in the bone marrow and bloodstream, crowding out healthy white and red blood cells and platelets.

As leukemia progresses, the effects on the body include:

  • Frequent infections, from a lack of healthy white blood cells
  • Anemia, from a lack of healthy red blood cells
  • Easy bruising and bleeding, because of inadequate platelets


Leukemia occurs most often in older adults. It is slightly more common in men than in women.

Although leukemia is the most common childhood cancer, overall, it is rare in children.

The National Cancer Institute estimates there were 52,380 new cases of leukemia, and 24,090 deaths caused by leukemia, in the United States in 2014.

In 2011, the most recent year for which statistics are available, an estimated 302,800 people were living with leukemia in the United States.

Worldwide, leukemia developed in 352,000 people and caused 265,000 deaths in 2012, according to the World Cancer Report, published by the World Health Organization.


Between 2004 and 2010, just over 57 percent of Americans with leukemia were still alive five years after diagnosis, according to the National Cancer Institute.

Death rates are higher among the elderly, with the percent of leukemia deaths highest among people ages 75 to 84.

Survival rates also vary widely among types of leukemia.

Risk Factors

Most cancers are caused by genetic mutations that arise for no known reason.

There are, however, some risk factors for developing leukemia as an adult. They include:

  • Being male
  • Being white
  • Being older than 70
  • Having received chemotherapy or radiation therapy in the past
  • Past exposure to high doses of radiation from other sources
  • Past exposure to high levels of solvents such as benzene
  • Having certain genetic disorders such as Down syndrome
  • Having myelodysplastic syndrome, a type of bone marrow disorder
  • Smoking

Types of Leukemia

Leukemias are named according to the type of white blood cell affected and whether they progress quickly (acute) or slowly (chronic).

White blood cells are categorized as either lymphoid or myeloid, depending on the type of stem cell from which they originated.

Lymphoid stem cells become lymphoblasts, which then mature into T lymphocytes (T cells), B lymphocytes (B cells), or natural killer (NK) cells.

Myeloid stem cells become red blood cells, platelets, or myeloblasts, which further mature into white blood cells called granulocytes and monocytes.

There are four main types of leukemia that occur in adults:

Acute lymphoblastic leukemia (ALL): In ALL, lymphoblasts fail to mature and instead reproduce rapidly, taking over the bone marrow.

ALL is the most common type of leukemia in children but is rare in adults.

Acute myeloid (or myelogenous) leukemia (AML): AML occurs when myeloid stem cells become abnormal myeloblasts that do not mature into healthy white blood cells.

In some cases of AML, a large number of myeloid stem cells become abnormal red blood cells or platelets.

AML is the most common type of acute leukemia in adults.

Chronic lymphocytic leukemia (CLL): In CLL, abnormal B cells (or, rarely, T cells) are produced.

CLL is the most common type of chronic leukemia in adults.

Chronic myeloid (or myelogenous) leukemia (CML): In CML, a genetic mutation called the Philadelphia chromosome causes production of excessive numbers of myeloid cells.

CML is a rare form of leukemia: Of all new U.S. cases of leukemia, roughly 10 percent are CML, according to the American Cancer Society.