Overview of Cytopenia
Cancer patients frequently develop cytopenia, a disorder in which the production of one or more blood cell types ceases or is greatly reduced. Cancer and chemotherapy used to treat cancer, and sometimes radiation therapy, can cause cytopenia.
Types of Cytopenia
A deficiency of red blood cells is called anemia; a deficiency of white blood cells, or leukocytes, leukopenia or neutropenia (neutrophils make up over half of all white blood cells); and deficiency of platelets, thrombocytopenia.
Pancytopenia is the deficiency of all three blood cell types and is characteristic of aplastic anemia, a potentially life-threatening disorder that requires a stem cell transplant.
The blood consists of three types of cells: red blood cells (erythrocytes), white blood cells (leukocytes), and platelets. Erythrocytes contain hemoglobin, the protein that carries oxygen from the lungs to all cells in the body. Proper cell function depends on an adequate oxygen supply. When cells are oxygen deprived, organ function can be seriously impaired.
Leukocytes (white blood cells) protect the body against viral, bacterial, and parasitic infection and detect and remove damaged, dying, or dead tissues. Someone with a deficiency of white blood cells is extremely vulnerable to infection.
The term "leukocyte" refers to all six types of white blood cells; each plays a unique role in the immune system:
- Basophils circulate in the blood and initiate the inflammatory response.
- Eosinophils kill infecting parasites and produce allergic reactions.
- Lymphocytes produce antibodies and regulate immune responses.
- Mast cells are fixed in tissues and initiate the inflammatory response.
- Monocytes capture infecting organisms for identification, ingest infecting organisms, and remove damaged or dying cells and cell debris. When monocytes become fixed in tissue, they are called macrophages.
- Neutrophils identify and kill infecting organisms, and remove dead tissue.
Platelets are essential factors for blood clotting. Sudden blood loss triggers platelet activity at the site of the wound. Exposure to oxygen in the air causes platelets to break apart and combine with a substance called fibrinogen to form fibrin. Fibrin has a thread-like structure and forms a scab, or external clot, as it dries. Platelet deficiency causes one to bruise and bleed easily. Blood does not clot at an open wound, and there is greater risk for internal bleeding.
All blood cells have a lifespan: erythrocytes have a lifespan of about 120 days; leukocytes, 1 to 3 days; and platelets, approximately 10 days. The body continually replenishes the blood supply through a process called hematopoiesis.
Blood Cell Formation—Hematopoiesis, the formation and development of blood cells, occurs in bone marrow. Bone marrow is a nutrient-rich spongy tissue located mainly in the central portions of long flat bones (e.g., sternum, pelvic bones) in adults and all bones in infants.
All blood cells derive from blood-forming stem cells that reside in bone marrow. Stem cells replicate indefinitely and develop into mature, specialized cells. A hormone produced in the kidneys, erythropoietin, stimulates blood stem cells to produce all three types of blood cells.