Leukemia is a blood cancer that starts in the bone marrow, where blood cells are made.

What kind of cancer it is

  • It is most often a cancer of white blood cells.
  • Doctors classify leukemia by how fast it grows: acute or chronic.
  • They also classify it by the blood cell line involved: lymphoid or myeloid.

Main types

The four main types are:

  1. ALL — acute lymphocytic leukemia.
  1. AML — acute myeloid leukemia.
  1. CLL — chronic lymphocytic leukemia.
  1. CML — chronic myeloid leukemia.

Simple way to think about it

Leukemia is not one single disease; it is a group of related cancers that affect blood-forming cells and can behave very differently depending on the type.

Bottom line: leukemia is a cancer of the blood and bone marrow, usually involving white blood cells.