Leukemia

Leukemia is a cancer of the blood that causes the cell lines in bone marrow to grow abnormally. This term refers mostly to white blood cells (leukocytes) and is used rarely in reference to red blood cells and platelets. White blood cells are the cells in the blood and tissues that protect animals from infection. With each injury or infection, these cells create a response to help protect the body from invading pathogens. Without them, a person has difficulty surviving. Overall, leukemia is divided into four broad categories. First, it is divided into myelogenous and lymphocytic, which are the two major different types of white blood cells. Myelogenous cells differentiate into many other types of white blood cells including neutrophils, eosinophils, and macrophages. Lymphocytic cells differentiate into B lymphocytes and T lymphocytes. Each of these two groups is further subdivided into acute and chronic diseases. An acute leukemia is normally a rapidly progressing disease that is caused by the overproduction of immature cells. A chronic leukemia has a more gradual onset and is caused by the overproduction of mature cells. A chronic leukemia can become an acute leukemia, but the reverse will not happen. An acute leukemia is generally more ominous, especially when it is preceded by a chronic leukemia. Death can occur within months after the onset of an acute leukemia if treatment is not sought. Approximately 70 percent of leukemias occur in adults and are mostly chronic lymphocytic leukemia and acute mylogenous leukemia. The remaining 30 percent is mostly acute lymphoblastic leukemia in children.

Human cells with acute myelocytic leukemia (AML) in the pericardial fluid, shown with an esterase stain at 400x.

All three groups of blood products—white blood cells, red blood cells, and platelets—are produced in the bone marrow. When the white blood cells outgrow the red blood cells and platelets, the other two groups are not able to produce their respective blood products because of the lack of room in the bone marrow. Thus, the signs and symptoms of leukemia reflect the shift of cells in the bone marrow, which normally allows growth of red blood cells, platelets, and white [Page 1014]blood cells to the uncontrolled growth of one line of cells. Many people with leukemia will present with weakness, fatigue, bruising, infection, and abnormal bleeding such as nose bleeds or around the gums. The fatigue is from the decreased number of red blood cells, also known as anemia. The bleeding and bruising is from a decreased number of platelets, which help the blood to clot. The increased number of infections is due to the dysfunctional white blood cells. Although there are more white blood cells than normal in the blood in leukemias, they do not function like a normal protective cell. Other nonspecific symptoms include fever, night sweats, and loss of appetite.

Diagnosis of leukemia is usually made from a complete blood count (CBC), a smear of the blood onto a microscope slide (peripheral smear), a bone marrow biopsy plated onto microscope slides, and genetic testing for cell markers (CD or cluster of differentiation) or translocation. Translocation is the joining of two halves of two different chromosomes that do not belong together and is usually determined by a process call fluorescent in situ hybridization (FISH). FISH is completed by looking at the 23 sets of human chromosomes and attaching a fluorescent marker to genes that are found on certain chromosomes. If the two markers end up on the same set of chromosomes, then there was no translocation. However, if the markers end up on different sets of chromosomes, then translocation is present. Examples of translocation would be the merging of a part of chromosome 9 with a part of chromosome 22 in acute lymphocytic leukemia and chronic mylogenous leukemia or the joining of part of chromosome 15 with part of chromosome 17 in acute myelocytic leukemia.

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