Leukemia

From the Greek words for white (leukos) and blood (hemia), leukemia refers to abnormally shaped and functioning leukocytes (white blood cells). Because the leukocytes multiply at an uncontrolled and rapid rate , leukemia is considered a cancer of the blood. Leukemia is neither contagious nor infectious, nor acquired from the mother prior to or during birth , but some researchers have suggested genetic predispositions exist for rare forms of leukemia, such as hairy-cell leukemia (HCL) that affects lymphocytes. Emerging evidence links leukemia to the Human T-Cell Lymphotropic Virus (HTLV), the Epstein-Barr Virus (EBV), and even HIV, although causes and risk factors are still poorly understood and fervently contested among scientists. Current research points to the cause of leukemia as a result of an acquired genetic injury to the DNA of a cell , which then multiplies in its damaged form until the disease state is reached.

Leukemia begins in the bone marrow and spreads through the lymph and blood system to tissues, organs, and sometimes testicles, brain , and spinal fluid. Leukocytes normally attack, kill, and help to expel invading microbes, but the leukocytes of patients with leukemia are abnormally shaped, increased in number, and immature of development (termed lymphoblasts). As the lymphoblasts multiply and spread, they outnumber and overwhelm the erythrocytes that transport oxygen and carbon dioxide in opposite directions, and hamper the function of platelets (thrombocytes), which help blood to clot.

History

In 1827, French physician Alfred Velpeau autopsied the body of a man who had experienced fever, weakness, pain , pus-filled blood, and headaches, and whose spleen weighed 10 lb (4.5 kg). Twelve years later, two more French physicians reported similar cases of fever, weakness, and enlarged organs, but suggested that the "pus-filled blood" actually contained white blood cells, or leukocytes. Scottish physicians found leukocytes when they conducted several more autopsies in 1845, including a man whose liver and spleen weighed 11 lb (4.9 kg) and 8 lb (3.6 kg), respectively. Also in 1845, German pathologist Rudolph Virchow coined a new term, weisses blut (white blood) to describe an imbalance between leukocytes and red blood cells, or erythrocytes. In 1890, another German physician, Paul Ehrlich, discovered that leukocytes varied by shape, kind, and function. In 1910, the same year that he discovered Salvarsan, the first "magic bullet" used against syphilis, Ehrlich discovered the poisonous extracts of mustard plants that were eventually developed into the first biological weapons. When inhaled, these "mustard gases" badly damaged lymph glands and the bone marrow, where white blood cells originate.

The French physicist Pierre Curie had weakness and swollen organs and glands until he was killed in 1906 by a horse-drawn carriage. In 1903, he and his Polish wife, Marie Curie (along with Henri Becquerel) shared the Nobel Prize in Physics . Following her discovery of the highly radioactive materials radium and polonium (she coined the term "radioactivity"), Marie Curie pioneered the battlefield use of primitive x-ray machines (protected only by fabric gloves and a thin metal screen) to locate bullets and shrapnel in wounded soldiers. Curie died in 1934 after experiencing the same pain and headaches, fatigue, swollen glands and organs—as did her daughter and son-in-law. Neither scientist linked his or her symptoms to the burns they experienced with each exposure to radium.

When Velpeau first peered through his microscope in 1827 at his "globules of pus in the blood," he was actually seeing leukemia, a disease name given by Virchow in 1847. The fevers, headaches, engorged glands, and swollen organs that those French, German and Scottish patients had developed, and the cause of Marie Curie's death, were leukemia. The disease that the American researchers were trying in 1942 to treat with highly toxic chemical therapies (nitrogen mustard), in extension of Ehrlich's earlier work with mustard plant extracts, was also leukemia.

Leukemia types and treatment

Leukemia specialists recognize four types of the disease. Distinctions between acute and chronic stages of leukemia depend upon the number and ratio of lymphoblasts (immature leukocytes), erythrocytes, and thrombocytes (platelets). Acute myeloid leukemia (AML) and acute lymphocytic leukemia (ALL) were diagnosed in 13,200 Americans in 1999, whereas chronic lymphocytic leukemia (CLL) and chronic myeloid leukemia (CML) accounted for 12,300 more cases in the same year. Another 4,600 Americans were diagnosed with rare forms such as erythroleukemia (affecting red blood cells), hairy-cell leukemia (HCL) and monocytic leukemia. Patients with leukemia can experience thrombocytopenia (insufficient platelets), which causes internal bleeding and excessive bruising, anemia (insufficient erythrocytes), which results in weakness, pale complexion, and dizziness due to insufficient oxygen, and leukopenia (insufficient disease-fighting leukocytes), which allows recurrent fevers and infections.

Due to increased skills, new technologies, and greater public awareness, more leukemia cases are being diagnosed. Leukemia accounts for nearly one-third of all new cases of cancer in children, but most cases are diagnosed in adults. Five-year survival rates for most forms of leukemia have dramatically risen, from roughly 5% in the early 1960s to 38% by the mid-1970s and 1980s. After diagnosis , greater than 40% of all patients with leukemia now survive for at least five years.

Researchers suspect that genetic, behavioral, and especially environmental factors cause leukemia. Morbidity (sickness) and mortality (death) rates vary greatly by gender, race, ethnicity, geography, and socioeconomic class. Forms of ionizing radiation , such as what Japanese survivors of atomic bombing experienced, are implicated strongly in three major forms of leukemia, but nonionizing forms of radiation (present in electricity ) have also been linked to leukemia's epidemiology , or disease patterns across time . Exposure to benzene , which occurs in petroleum , chemical, shoe, and rubber manufacturing, and in painting and printing , correlates strongly to leukemia, but its use has been banned in the United States since 1945, although it is used elsewhere. Long-term exposure to agricultural fertilizers and infectious agents associated with livestock , pesticides , and diesel fuel and exhaust, have all been suggested as risk factors for the development of leukemia.

Both improved and new therapies have greatly reduced morbidity and mortality from leukemia. The hormone erythropoietin, for example, helps oxygen-carrying erythrocytes to multiply, which might help to treat some leukemia-caused anemias. Standard treatment options range from chemotherapy to biological therapies, from surgery to radiation, from radiation and chemotherapy combined to marrow stem cell transplantation. Surgery can be used to remove swollen and enlarged lymph nodes

or organs such as the spleen that cause severely decreased platelets in the bone marrow and bloodstream. Drug therapy is usually the first option, and the ultimate goal is complete remission, in which no lymphoblasts are seen in the blood and bone marrow is normal. Biotherapy (immunotherapy) works with synthesized forms of naturally occurring substances in the body (interferon and interleukins) to disrupt the multiplication and spread of immature cells (lymphoblasts). Homeopathic remedies treat leukemia as a character trait, as the body's expression of an insult to the system. Due to earlier detection and improved therapies, leukemia is no longer considered a virtual death sentence, and many people remain in remission decades after treatment.

See also Lymphatic system.

Resources

books

Lackritz, Barbara. Adult Leukemia: A Comprehensive Guide for Patients and Families. Cambridge: O'Reilly, 2001.

Teeley, Peter, and Philip Bashe. The Complete Cancer Survival Guide. New York: Doubleday, 2000.

periodicals

Christensen, Damaris. "Old drug, New uses?" Science News 162, (2002): 296–98.

organizations

Leukemia and Lymphoma Society. 1311 Mamaroneck Ave. White Plains, NY 10605 (914) 949–5213. <http://www.leukemia.org/hm_lls>.

other

Reynal, Florence. "Marie Curie: A Nobel Prize Pioneer at the Pantheon." August 1995 [cited January 22, 2003].

<http://www.france.diplomatie.fr/label_france/index/gb/sciences-techno01.html>

Lawrence Hammar

KEY TERMS

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Lymphoblast

—Immature white blood cells.

Lymphocyte

—White blood cells that originate in the spongy tissue of the bone marrow.

Marrow stem cell

—Immature blood-forming cells, normally fewer than one in 100,000 of the cells in the bone marrow.

Remission

—A period of time when neither disease causes nor associated symptoms can be found.