Hematology of Leukemia
The Woburn Toxic Trial focused on a suspected childhood leukemia cancer cluster and its connection to pollutants in the municipal water supply. This webpage includes background information on the hematology of leukemia.
Components of Human Blood
Human blood is an amazing fluid. It consists of plasma and cells (red blood cells, white blood cells, and platelets) that supply nutrients and other elements to tissues and remove waste products. Blood also enables other cells and substances to be transported between tissues and organs, transfers heat to the skin, and acts as a buffer to regulate pH. About five liters of blood circulate in an average adult. Blood is created solely by the marrow inside bones.
Red blood cells are the most common type of blood cell and are the body's principal means of delivering oxygen from the lungs to tissues. White blood cells (also known as leukocytes) help the body defend against infectious disease and foreign materials as part of its immune system. Platelets cause blood to clot.
Leukemia – Cancer of the Blood
Leukemia is a disease of the white blood cells. A leukemia patient has an elevated white blood cell count consisting largely of immature and unhealthy white blood cells. Normal bone marrow cells are displaced by increasing numbers of the malignant cells, which results in a lack of blood platelets and regular white blood cells needed to clot blood and fight infection.
Leukemia is categorized as either acute or chronic. In acute leukemia, immature blood cells rapidly grow and the bone marrow is unable to produce healthy blood cells. In chronic leukemia, there is an excessive buildup of relatively mature, but abnormal, blood cells. Chronic leukemias typically take months or years to progress. Leukemia is also classified by the type of abnormal blood cell found most often. When leukemia affects lymphoid cells, it is considered lymphocytic leukemia. When myeloid cells are affected, it is considered myelgenous leukemia.
Combining these two types of categories, leukemia is further categorized as:
- Acute lymphocytic leukemia (ALL), which is also known as acute lymphoblastic leukemia). ALL is the most common type of leukemia found in children. The disease also affects adults, particularly those over 65 years of age.
- Acute mylogenous leukemia (AML) is more common in adults than in children.
- Chronic lymphocytic leukemia (CLL) occurs most often in adults over the age of 55.
- Chronic myelogenous leukemia (CML) occurs in adults, with a very small number of children developing this disease.
The causes of leukemia are unknown but genetic and environmental factors are involved. Some studies link leukemia to exposure to high doses of radiation and petrochemicals. Higher leukemia rates are found in more developed countries and in higher socioeconomic groups.
Acute Lymphocytic Leukemia
ALL is the type of leukemia most often found in children under the age of 19. About 3,970 cases are diagnosed each year in the United States. ALL results from an injury to the DNA of a cell in the bone marrow. A leukemic cell replaces normal bone marrow, which leads to:
- Uncontrolled and exaggerated growth and accumulation of cells ("lymphoblasts" or "leukemic blasts". These cells don't function as normal blood cells.
- Blockage of normal bone marrow cells, leading to a deficiency of red cells (anemia), platelets (thrombocytopenia), and normal white cells (especially neutrophils) in the blood.
- Possible symptoms of childhood ALL include: fever, easy bruising or bleeding, petechiae (flat, pinpoint spots under the skin caused by bleeding), bone or joint pain, painless lumps in the neck, underarm, stomach, or groin, pain or feeling of fullness below the ribs, weakness or feeling tired, and loss of appetite.
The two images at left are from needle aspiration biopsies of human bone marrow, a medical procedure that pierces the bone marrow with a thin needle to collect cells for examination. The cells are then smeared on a slide for examination under a microscope. The image on the left shows normal bone