Leukemia, Part 1 — Introduction, Incidence and Symptoms

What is leukemia?

Leukemia is the most common type of cancer in children. All cancers begin in cells of the body, and leukemia is a cancer that begins in blood cells. Normally, cells grow and divide to form new cells as the body needs them. When cells grow old, they die and new cells take their place. Sometimes, this process does not work right. In cancer, new cells form when the body does not need them, and old cells do not die when they should.

Leukemia is a cancer that involves the blood-forming tissues of the bone marrow, spleen and lymph nodes. It is characterized by an uncontrolled production of abnormal, immature blood cells. There are different kinds of childhood leukemia. The most common type is called acute lymphoblastic leukemia (aka acute lymphocytic leukemia or ALL). In this disease, too many underdeveloped infection-fighting white blood cells or lymphocytes (LIM'-foh-syts) are present in the blood and bone marrow of a child. ALL is the most common kind of leukemia in children and the most common form of all types of cancer in children.

The bone marrow is the site where lymphocytes and other blood cells are made. It is a spongy tissue found inside many large bones of the body. The bone marrow produces three types of blood cells:  Red blood cells contain hemoglobin and carry oxygen and other materials to the tissues throughout the body; Platelets help to form clots; White blood cells help fight off infections in the body.

Leukemia cells in the blood.

When a person has leukemia, the bone marrow does not work properly. The bone marrow produces abnormal, immature cells, called leukemia cells. Leukemia cells are commonly referred to as "blasts". These immature cancer cells crowd out other blood-forming cells in the bone marrow. If a child's bone marrow is not able to make enough red blood cells to carry oxygen, the child may develop anemia, and feel very tired. If sufficient platelets are not produced, the blood will not clot properly and the child may bleed or bruise easily. When white blood cells are not plentiful enough, the body cannot fight off germs and the child may develop frequent infections.

Leukemia can be either acute (progressing quickly) or chronic (progressing more slowly). Most children have an acute form of leukemia.

Incidence and prevalence

Acute lymphoblastic leukemia (ALL) is the most common malignancy of childhood, representing nearly one-third of all pediatric cancers. In the U.S., about 2,000 new cases of ALL are diagnosed each year. The incidence peaks between the ages of 2 and 5, and is slightly more likely among male children. The annual incidence of ALL among children younger than 15 is: 33 cases per million for whites, and 15 cases per million for blacks. The cause of most cases of leukemia remains unknown.


Early symptoms of leukemia are caused by the decrease in the number of mature, functional red blood cells, white blood cells and platelets. These symptoms can include:

  • fevers or night sweats
  • frequent infections
  • feeling weak or tired
  • headache
  • bleeding and bruising easily (e.g., bleeding gums, purplish patches or tiny red spots in the skin)
  • pain in the bones or joints
  • swelling or discomfort in the abdomen
  • swollen lymph nodes, especially in the neck or armpit
  • weight loss

These symptoms do not necessarily mean a person has leukemia. Other problems, such as infections, can cause similar symptoms. If these symptoms are due to leukemia, a blood test would show unusual numbers of blood cells. Additional tests would confirm the diagnosis.

For more information

Part 2 — Treatment, Side Effects, Restrictions, and Implications for School


Leukemia and Lymphoma Society

National Cancer Institute

Contributed by:

Mukta Kumar, MD
Assistant Professor
Section Chief
Division of Pediatric Hematology and Oncology
Department of Pediatrics
University of Kansas Medical Center

Kathy Davis, MSEd, PhD
Associate Professor
Project Director, Connected Kansas Kids
Director, KU Kids Healing Place
University of Kansas Medical Center