Leukemia is a disease of the blood

Blood is a vital liquid that carries oxygen, food, hormones, and other necessary
chemicals to all of the body’s cells. It also removes toxins and other waste products
from the cells. Blood helps the lymph system fight infection and carries the cells
necessary for repairing injuries. Blood also contains important clotting factors.
Whole blood is made up of plasma, which is a clear fluid, and many other compo-
nents, each with a specific task. All three types of blood cells are affected by leukemia:
red blood cells, platelets, and white blood cells.
Red blood cells (erythrocytes or RBCs) contain hemoglobin, a protein that picks up
oxygen in the lungs and transports it throughout the body. RBCs that contain oxygen
give blood its red color. When leukemia cells in the bone marrow slow down the
production of red cells, the child develops anemia. Anemia can cause tiredness, weak-
ness, irritability, pale skin, and headache: all due to decreased oxygen being carried to
the body tissues.
Platelets (thrombocytes) are tiny, disc-shaped cells that help form clots to stop
bleeding. Leukemia can dramatically slow down the production of platelets, causing
children to bleed excessively from cuts or from the nose or gums. Children with leuke-
mia can develop large bruises (ecchymoses) or small red dots (petechiae) on their skin.
White blood cells (leukocytes or WBCs) destroy foreign substances in the body such
as viruses, bacteria, and fungi. WBCs are produced and stored in the bone marrow
and lymph nodes. They are released when needed by the body. If an infection is
present, the body produces extra WBCs. There are three main types of WBCs:
• Lymphocytes. Two types of lymphocytes interact to prevent infection, fight
viruses and fungi, and provide immunity to disease:
– T cells attack infected cells, foreign tissue, and cancer cells.
– B cells produce antibodies that destroy foreign substances.
• Granulocytes. There are three types of granulocytes:
– Neutrophils attack foreign bacteria.
– Eosinophils respond to allergic reactions as well as foreign
bacteria and parasites.
– Basophils are the rarest of the white cells and play a special
role in allergic reactions.
• Monocytes. Monocytes are cells that scavenge (clean up) waste material that is
left over from battles between the body’s defenses and infectious or cancerous
invaders. They also contain enzymes that kill foreign bacteria.
The different types of leukemia are cancers of a specific white blood cell type. For
instance, acute lymphoblastic leukemia affects only lymphocytes. The specific types
of leukemia are explained later in the chapter.
Definition of a blast
“Blast” is a short name for an immature white blood cell such as lymphoblast, myelo-
blast, or monoblast. Normally, less than 5 percent of the cells contained in healthy
bone marrow at any one time are blasts. Normal blasts develop into mature, function-
ing white blood cells, and are not usually found in the bloodstream. Leukemic blasts
remain immature, multiply continuously, provide no defense against infection, and
may be present in large numbers in the bloodstream and bone marrow.
When leukemia begins
When abnormal blasts appear in the bone marrow, they multiply rapidly and lose
their ability to grow up into normal white cells. They begin to crowd out the normal
cells that usually develop there. After accumulating in the bone marrow, leukemic
cells spill over into the blood. Leukemic cells may also cross the blood-brain barrier
and invade the central nervous system (brain and spinal cord).
When leukemic blasts begin to fill the marrow, production of healthy red cells, plate-
lets, and white cells cannot be maintained. As the number of normal cells decreases,
symptoms appear. Low red cell counts cause fatigue and pale skin. Low platelet
counts may result in bruising and bleeding problems. If mature neutrophils and lym-
phocytes are crowded out by the blasts, the child will have little or no defense against
infections.