Leukemia is cancer of blood cells. There are several types of blood cells, including red blood cells (RBC), white blood cells (WBC) and platelets. Generally, leukemia refers to cancer of white blood cells.
White blood cells are an important part of the immune system. They can protect your body from bacteria, viruses and fungi, as well as abnormal cells and other foreign bodies. In leukemia, white blood cells do not function like normal white blood cells. They may also divide too fast and eventually crowd out normal cells.