Leukemia, first recognised by the German pathologist Rudolf Virchow in 1847, starts with tissues such as bone marrow behaving abnormally. This is caused by a mutation in its DNA. Bone marrow stem cells produce billions of red blood cells and white blood cells each day, respectively carrying oxygen and fighting disease around all parts of the body. Leukemia is characterised by an excessive production of abnormal versions of these cells, overcrowding the bone marrow. This results in decreased production and function of normal blood cells. Leukemia can spread to the lymph nodes, spleen, liver, central nervous system and other organs.
Scientists are still actively searching for the exact cause of leukemia. The bone marrow stem cells are thought to become cancerous because of mutation to their DNA. This could come from exposure to radiation, carcinogenic substances, or translocation (swapping) of genetic material in the chromosomes. It is possible to test whether some of these translocations have occurred in a person's chromosome, confirming whether they have or are likely to develop leukemia. Similar genetic tests can also determine the aggressiveness needed in treatment and also the expected prognosis.
Viruses have also been linked, with varying levels of speculation, to some forms of leukemia. T-cell leukemia has recently been confirmed to be the result of two viruses.
In the early 1990s concern was raised in the UK about the effect of nuclear power plants on unborn children, when clusters of leukemia cases were discovered nearby to some of these plants. The effect was speculative because clusters were also found where no nuclear plants were present, and not all plants had clusters around them. Using statistical analysis researchers at Southampton University concluded that a link was present, deducing that radiation damage to men working at the plants had caused genetic abnormalities in their children. After this report British Nuclear Fuels initially advised workers who were being exposed to high levels of radiation not to father children, although they have since withdrawn this advice.
As with all cancers, leukemia is a broad term covering a spectrum of diseases. In leukemia, the diseases are classified according to the type of abnormal cell found most in the blood. Leukemia is also clinically split in to its acute and chronic forms. The four main forms are:
- Acute lymphocytic leukemia (ALL)
- Acute myelogenous leukemia (AML)
- Chronic lymphocytic leukemia (CLL)
- Chronic myelogenous leukemia (CML)
The most common forms in adults are AML and CML, whereas in children ALL is most widely observed.
Acute leukemias are characterised by the rapid growth of immature blood cells, which then die early (within one to five months.) This crowding makes the bone marrow unable to produce healthy blood cells. Acute forms of leukemia are most common in children and young adults (in fact it is a more common cause of death for children in the US than any other type of malignant disease.)
Chronic leukemias are distinguished by the slower excessive buildup of mature, but still abnormal, blood cells. Typically taking two to five years to progress, the cells live too long, meaning too many mostly white blood cells form in the blood. Chronic leukemia mostly appears in older people. Whereas acute leukemia must be treated immediately, chronic forms are sometimes monitored for some time before treatment to ensure maximum effectiveness of therapy.
Damage to the bone marrow results in a lack of blood platelets, which are important in the blood clotting process. This means people with leukemia may become bruised or bleed excessively. Similarly, the blood cell deficiency leads to shortness of breath and fatigue (blood cells are needed to carry oxygen efficiently around the body). Bone or joint pain may occur, possibly because of cancer spreading to these areas. Headaches and vomiting are indicative of the cancer having dispersed to the central nervous system.
In the case of acute myelogenous leukemia, small rash-like spots on the skin as well as enlarged gums are typically evident. Acute lymphocytic leukemia can cause the thymus to become enlarged, and can mean severe coughing or even suffocation. Chronic myelocytic leukemia can lead to enlargement of the spleen. Chronic lymphotic leukemia can manifest itself as oversized lymph node.
Major treatments include chemotherapy and radiation therapy. These are typically used in combination to maximise effectiveness and reduce any particular side effect. Because of the severity of some courses, bone marrow transplants are sometimes necessary. Healthy bone marrow transplanted in to the body helps rebuild tissue damaged by the treatment.
27,900 adults and 2,300 children are diagnosed each year with leukemia in the US. Over the last thirty years, the chances of survival have doubled, although they remain still quite low. These range from a 22 per cent survival rate in 1970 to 43 per cent rate in the 1990s.