Childhood acute lymphoblastic leukemia (ALL) is a type of cancer in which the bone marrow makes too many immature lymphocytes (a type of white blood cell).

Childhood acute lymphoblastic leukemia (also called ALL or acute lymphocytic leukemia) is a cancer of the blood and bone marrow. This type of cancer usually gets worse quickly if it is not treated.

ALL is the most common type of cancer in children.

Leukemia may affect red blood cells, white blood cells, and platelets.

In a healthy child, the bone marrow makes blood stem cells (immature cells) that become mature blood cells over time. A blood stem cell may become a myeloid stem cell or a lymphoid stem cell.

A myeloid stem cell becomes one of three types of mature blood cells:

A lymphoid stem cell becomes a lymphoblast cell and then one of three types of lymphocytes (white blood cells):

In a child with ALL, too many stem cells become lymphoblasts, B lymphocytes, or T lymphocytes. These cells are cancer (leukemia) cells. The leukemia cells do not work like normal lymphocytes and are not able to fight infection very well. Also, as the number of leukemia cells increases in the blood and bone marrow, there is less room for healthy white blood cells, red blood cells, and platelets. This may lead to infection, anemia, and easy bleeding.

This summary is about acute lymphoblastic leukemia in children, teenagers, and young adults. See the following PDQ summaries for information about other types of leukemia:

Adapted from the National Cancer Institute’s Physician Data Query (PDQ(r)) Cancer Information Summaries (http://www.cancer.gov/cancertopics/pdq). Date Last Modified: April 13, 2015