The abnormal proliferation of white blood cells causes a type of cancer known as leukemia. Leukemia is primarily caused by chromosomal instability, which leads to the transfer of genes from one chromosome to another, with or without fusion or juxtaposition of two different genes. This phenomenon is known as translocation and causes a change in the rate expression of the translocated genes. Translocations can therefore lead either to gene fusions or to the juxtaposition of oncogenes to other genes. At presently, it is known at least ten different types of gene fusion and nine types of juxtapositions associated with leukemia.
Leukemia itself is divided into two different types: lymphocytic leukemias and myelogenous leukemias. Lymphocytic leukemias occur when a given translocation affects lymphoid cells, which induces its overproduction and accumulation in lymphocytic tissues and lymph nodes, with the consequent spread to other areas of the body. When the translocation affects the rate of production of young myelogenous cells in the bone marrow, it also leads to an extramedullar production of these cells in the lymph nodes, spleen, and the liver. Myelogenous leukemia may occur under the form of neutrophilic, basophilic, eosinophilic, or monocytic subtypes, when the mutated cells are partially differentiated, i.e., have some degree of maturation and functional specialization. However, the majority of leukemia cases do present white cells without specialization, which are very different from their normal analogues.
Leukemia may also occur in two different forms: acute or chronic. Chronic leukemia is characterized by more differentiated cells and evolves slowly, over a period of 10-20 years, whereas the acute form is due to the production of more undifferentiated cells. Leukemic cells are usually ineffective in providing immune protection, as do their normal counterparts. Therefore, patients with leukemia are prone to infections, severe anemia, as well as hemorrhages (due to a decrease in blood platelets). Moreover, leukemic cells migrate to other tissues of the body (metastasis), such as bones, spleen, liver, and lymph nodes, where they rapidly overgrow and destroy the surrounding tissues. Because the metabolic rate of abnormally rapid-proliferating cells dramatically increases the demand for the nutrient reserves of the body (i.e., glucose, amino acids, vitamins), leukemia can induce a metabolic starvation of other tissues and organs.
New molecular treatments against most types of leukemia have being recently developed and have proved highly effective in controlling the disease, such as a drug that inhibits c-kit, an oncogene essential for the induction of leukemic cell-proliferation, as well as several redifferentiation arsenic-like compounds. However, these treatments do not imply cure. In the case of c-kit inhibitor, for instance, the drug has to be orally taken throughout the patient's life.
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