We have been greatly informed by Nancy Keane's book Childhood Leukemia: A Guide for Families, Friends, and Caregivers. The following information is taken directly from the second chapter of her book because I certainly couldn't write anything half so comprehensive and accessible.
The word leukemia literally means white blood. Leukemia is the term used to describe cancer of the blood-forming tissues known as bone marrow. This spongy material fills the bones in the body and produces blood cells. With leukemia, the bone marrow creates an overabundance of abnormal white cells. As the bone marrow becomes packed with these abnormal cells, they crowd out all the healthy cells that are needed for blood to do its work, and symptoms of the disease begin to develop.
Blood is a vital liquid that carries oxygen, food, hormones, and other necessary chemicals to the body's cells. It also removes toxins and other waste products from the cells. Blood helps the lymph system fight infections and carries the cells needed to repair injuries.
Whole blood is make up of plasma - a clear fluid - and many other components, each with a specific task. Blood also contains three types of blood cells (red blood cells, platelets, and white blood cells), all of which are affected by leukemia.
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 RBCs, anemia develops. Anemia can cause tiredness, weakness, irritability, pale skin, and headaches - 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 with the disease to bleed excessively from cuts or from the nose or gums. Children with leukemia can develop large bruises (ecchymoses) or small red dots (petechiae) on their skin.
Healthy 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. The two types of lymphocytes are T cells and B cells.
- Granulocytes. The three types of granulocytes are neutrophils, eosinophils, and basophils.
The different types of leukemia are cancers of a specific WBC type. For instance, acute lymphoblastic leukemia affects only lymphocytes.
Blast is a short name for an immature WBC, such as lymphoblast or monoblast. Normally, less than 5 percent of the cells in healthy bone marrow at any one time are blasts. While in the bone marrow, normal blasts develop into mature, functioning WBCs and are then released into the bloodstream. Therefore, in healthy people, blasts 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 abnormal blasts appear in the bone marrow, they multiply rapidly and lose their ability to develop into normal WBCs. They begin to crowd out the normal cells that grow from helathy blasts into mature WBCs. After accumulating in the bone marrow, leukemic blasts spill over into the blood and, if left unchecked, may invade the central nervous system (CNS), which includes the brain, spinal cord, and other organs.
When leukemic blasts begin to fill the marrow, production of healthy RBCs, platelets, and WBCs cannot be maintained. As the number of normal blood cells decreases, symptoms appear. Low RBC counts cause fatigue and pale skin. Low platelet counts may result in bruising and bleeding problems. And if mature neutrophils and lymphocytes are crowded out by blasts, the child will have little or no defense against infections.
Leukemia is described as either acute (progressing quickly) or chronic (progressing slowly and usually involving more mature cells). The acute leukemias, which comprise about 95 percent of all childhood leukemias, are further divided into acute lymphoblastic leukemia (ALL), in which the cancerous cells are lymphocytes, and acute myeloid leukemia (AML), in which the granulocytes or monocytes malfunction.
Seventy-five percent of all children with leukemia have ALL. It is caused by a rapid increase of immature lymphocytes (lymphoblasts), which would normally have developed in to mature WBCs. There are several subgroups of ALL, which are based on whether the cancer cells developed from cells that would have become B cells or T cells.
Maggie has common precursor B cell ALL. The majority of children with B-lineage ALL have this type, which carries the best prognosis of all types of ALL.