What is Childhood Leukemia?
Leukemia is a cancer of the early blood-forming cells. Usually, the leukemia is a cancer of the white blood cells, but leukemia can involve other blood cell types as well.
Leukemia starts in the and then spreads to the blood. From there it can go to the lymph nodes, spleen, liver, central nervous system (the brain and spinal cord), testes (testicles), or other organs.
Some childhood cancers, such as neuroblastoma or Wilms tumor, start in other organs and can spread to bone marrow, but these cancers are not leukemia.
The bone marrow is the inner part of bones. It is where blood cells (red blood cells, white blood cells and platelets) are produced. In infants, active bone marrow is found in almost all bones of the body, but by the teenage years, it is found mainly in the flat bones (skull, shoulder blade, ribs, pelvis) and vertebrae (back bones).
The bone marrow is made up of (hematopoietic) cells and supporting tissues that aid the growth of blood-forming cells. The earliest blood-forming cells are called . These cells can either divide to produce more stem cells or grow into other blood cells namely, the , , and .
carry oxygen from the lungs to all other tissues of the body. When the marrow does not produce enough red blood cells to replace those wearing out, a condition known as (too few red blood cells in the body) can result. Anemia typically causes weakness, paleness of the skin, tiredness, and shortness of breath.
are fragments that break off from a type of bone marrow cell called a
and are released into the bloodstream. Platelets are important in plugging areas of damage to small blood vessels caused by cuts or bruises. Not having enough platelets is called and can result in excessive bleeding and bruising.
, also known as leukocytes, defend the body against infections with bacteria and fungi (germs). The 3 main types of white blood cells are lymphocytes (discussed in the section on lymphoid tissue), granulocytes, and monocytes.
- come from an early cell called the . This is the malignant cell in . Granulocytes destroy germs such as bacteria. The main type of granulocyte is called a or . Two other types are , and . They are all distinguished by the size and color of their granules (spots seen inside the cells under the microscope). These granules contain chemicals that help fight invading microorganisms. Granulocytes undergo several changes as they mature from a primitive myeloblast to infection-fighting cells. Once released into the bloodstream as mature cells, they circulate for only a short period of time (usually just a few hours), so they must be constantly replaced.
- also protect the body against microorganisms. After circulating in the bloodstream, they enter tissues to become , which can destroy some germs by surrounding and digesting them. Macrophages also help lymphocytes recognize germs so they can make antibodies to fight them.
Lymphoid tissue, also known as lymphatic tissue, is the main component of the immune system. It is formed by several different types of cells that work together to resist infection. Lymphoid tissue and the immune system may also fight some types of cancers. This system also reacts to tissues received from other people, such as blood transfusions or organ transplants.
Lymphoid tissue is found in many places throughout the body, including the lymph nodes, thymus, spleen, tonsils and adenoids, and bone marrow. It is also scattered within other systems, such as the digestive system and respiratory system. There is an extensive interconnecting system between all lymphoid tissues called the lymphatic system. Lymphocytes circulate in this system and eventually flow into the bloodstream.
The is the main cell type that forms lymphoid tissue. These are the cells from which develops.
There are 2 main types of lymphocytes:
- B lymphocytes (B cells)
- T lymphocytes (T cells)
Although both can develop into leukemia, B-cell leukemias are much more common than T-cell leukemias.
Normal T cells and B cells do different jobs in the immune system.
help protect the body against bacteria and viruses by maturing into plasma cells and producing immunoglobulins (antibodies). Antibodies attach to certain chemicals on the surface of a germ. This attracts another type of cell (the granulocyte, discussed above), which digests the antibody-coated germ. Antibodies also attract certain proteins that can destroy bacteria by punching holes in them.
help protect us against foreign substances (those not normally present in the body). They recognize specific chemicals, such as those found on the outside of virus-infected cells. They then destroy these cells by releasing substances that cause them to develop holes and become leaky. T cells can also release substances called that attract other types of white blood cells, such as macrophages, which then surround and digest the infected cells.
T cells are also thought to destroy some types of cancer cells as well as the cells of transplanted organs. Patients with transplanted organs must take special medication to prevent this action by T cells.
Normal B cells and T cells can be recognized by laboratory tests that identify distinctive chemicals on their surfaces. Some chemical substances are found only on B cells, and others are found only on T cells.
There are actually several types of T cells, each with a specialized job to do. There are also several stages of B-cell and T-cell development or maturation that can be recognized. This is important because leukemias that arise from these cells tend to resemble a particular subtype of normal lymphocyte at a certain level of development.
Normal are bean-sized organs located throughout the body and
connected by a system of lymphatic vessels. These vessels are like thin veins, except that instead of carrying blood, they carry . Lymph is a clear fluid containing waste products and excess fluid from tissues, as well as immune system cells traveling between lymph nodes and other organs.
Lymph nodes enlarge when they are fighting an infection, especially in infants and children. Lymph nodes that grow during a reaction to infection are called or . An enlarged lymph node is not usually serious in a child. But a large lymph node may sometimes be a sign of leukemia.
The is located under the lower part of the rib cage, on the left side of the body. It is the largest collection of lymph tissue in the body. The spleen produces lymphocytes and other immune system cells to help fight infections. It also stores healthy blood cells and filters out damaged blood cells, bacteria, and cell waste. If certain diseases cause the bone marrow to stop producing blood cells, the spleen may function in a back-up role for this task.
The is an organ located in front of the heart. Before birth, this gland plays a vital role in development of the T lymphocytes, which are important to the immune system. Although the thymus gland's size and importance peak early in childhood, it continues to function in the immune system throughout life.
and are collections of lymphoid tissue located at the back of the throat. They are easy to see when they become enlarged during an infection or if they become cancerous.
