Leukemia is a form of cancer unlike any other, and one of the more dangerous. The term leukemia refers to cancers of the white blood cells (also called leukocytes or WBCs). Leukemia is cancer of your body's blood-forming tissues, including the bone marrow and lymph system. The word leukemia means "white blood" in Greek. The disease usually starts in the white blood cells.
Under normal circumstances, your white blood cells are potent infection fighters. These cells normally grow and divide in an orderly, controlled way, as your body needs them. But leukemia disrupts this process.
In people with leukemia, the bone marrow produces a large number of abnormal white blood cells. They look different from normal blood cells and don't function properly. Eventually, they block production of normal white blood cells, impairing the ability to fight off infection. Leukemia cells also crowd out other types of blood cells produced by the bone marrow, including red blood cells, which carry oxygen to tissues throughout the body, and platelets, which help form blood clots that control bleeding.
Leukemia isn't just a children's disease, as some people think. Leukemia has four main types and many subtypes - and only some of them are common among children. Overall, this form of cancer affects about 10 times as many adults as children. Leukemia is usually fatal without successful treatment.
Signs and symptoms
Signs and symptoms for each type of leukemia differ, but common symptoms include:
The severity of signs and symptoms depends on the number of abnormal blood cells and where they collect. Early symptoms of leukemia may be overlooked because they may resemble symptoms of the flu and other common illnesses.
Doctors classify leukemia in two ways. The first is by how fast the leukemia progresses:
The second type of classification is by type of white blood cell affected:
The major types of leukemia are:
Other, rarer types of leukemia include hairy cell leukemia and chronic myelomonocytic leukemia.
Doctors don't understand the exact cause of leukemia. It seems to develop from a combination of genetic and environmental factors.
Acute leukemia begins with one or a few white blood cells that have a lost or damaged DNA sequence. These cells remain immature in what's known as a blast form, but maintain the ability to multiply. Because they don't mature and then die as normal cells do, they accumulate and begin to interfere with functions of vital organs. Eventually, they overwhelm the production of healthy cells.
Chronic leukemia involves more mature blood cells. They replicate and accumulate more slowly, so the progression of the disease is slower but it can still be deadly. Experts aren't sure why this process begins.
Whatever the reason, having too few normal white blood cells eventually leads to infection, anemia and excessive bleeding. Having too many abnormal white blood cells can impair the function of bone marrow and infiltrate other organs. Death usually results from bleeding or infection.