Cancer is a group of many related diseases. All cancers begin in cells
, the body's basic unit of life. Cells make up tissues, and tissues make up the organs of the body.
Normally, cells grow and divide to form new cells as the body needs them. When cells grow old and die, new cells take their place. Sometimes this orderly process goes wrong. New cells form when the body does not need them, and old cells do not die when they should. These extra cells can form a mass of tissue called a growth or tumor
Tumors can be benign or malignant.
Benign tumors are not cancer.
Usually, doctors can remove them. Cells from benign tumors do not spread to other parts of the body. In most cases, benign tumors do not come back after they are removed. Most important, benign tumors are rarely a threat to life.
Malignant tumors are cancer.
They are generally more serious. Cancer cells can invade and damage nearby tissues and organs. Also, cancer cells can break away from a malignant tumor and enter the bloodstream or the lymphatic system. That is how cancer cells spread from the original (primary
) tumor to form new tumors in other organs. The spread of cancer is called metastasis
Leukemia is cancer that forms in blood-forming tissue such as bone marrow and causes blood cells to be produced and enter the bloodstream. It usually starts in white blood cells, which are strong infection fighters. This cancer causes blood cells to grow and divide abnormally, and therefore produces large numbers of white blood cells that do not function properly.
In the United States, more than 40,800 adults and 3,500 children are diagnosed with leukemia each year. People who are exposed to high levels of radiation and the chemical benzene are more likely to get certain types of leukemia, as are smokers, people who have had chemotherapy and people with certain inherited diseases and blood disorders.
Types of leukemia can be grouped based on how quickly the disease develops and worsens. Leukemia is either chronic
This type usually gets worse slowly. Early in the disease, the leukemia cells can still do some of the normal work of white blood cells. People often don't have symptoms at first, and the disease is usually found through routine check-ups or blood tests.
As the number of leukemia cells increases, symptoms such as swollen lymph nodes or infections start to appear. Symptoms are mild at first but slowly get worse.
- This type usually gets worse quickly. The leukemia cells can't do the work of normal white blood cells, and the number of leukemia cells increases rapidly.
Leukemia types can also be grouped by the type of white blood cell that is affected.
Leukemia that affects lymphoid cells is called lymphoid, lymphocytic or lymphoblastic leukemia.
Leukemia that affects myeloid cells is called myeloid, myelogenous or myeloblastic leukemia.
Four Common Types Of Leukemia
Chronic Lymphocytic Leukemia (CLL):
CLL affects lymphoid cells and grows slowly. Most often, this is diagnosed in people over the age of 55 and rarely affects children.
Chronic Myeloid Leukemia (CML):
CML affects myeloid cells and tends to grow slowly at first. It mainly affects adults.
Acute Lymphocytic (lymphoblastic) Leukemia (ALL):
ALL affects lymphoid cells and usually grows quickly. This is the most common leukemia found in children, but it also affects adults.
Acute Myeloid Leukemia (AML):
AML affects myeloid cells and grows quickly. It occurs in both children and adults.
Another form of leukemia, called hairy cell leukemia
, is a rare type of chronic leukemia.