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National Cancer Institute: (http://www.nci.nih.gov) One of the many Institutes that makes up the National Institutes of Health. Each Institute is dedicated to research on the causes, behavior, treatment, and prevention of human diseases. The Institutes is part of the Public Health Service and resides administratively in the Department of Health and Human Services. The home page of the National Institutes of Health can be found at http://www.nih.gov.

Neutropenia: A decrease below normal in the concentration of neutrophils, a type of white cell.

Neutrophils: The principal phagocyte (microbe-eating) cell in the blood. This blood cell is the main cell that combats infections. Often, it is not present in sufficient quantities in patients with acute leukemia or after chemotherapy. A severe deficiency of neutrophils increases the patient's susceptibility to infection. A neutrophil may be called a “poly” (polymorphonuclear neutrophil) or “seg” (segmented neutrophil) because its nucleus has several lobes.

Oncogene: A mutated gene that is the cause of a cancer. Several subtypes of acute myelogenous leukemia, acute lymphocytic leukemia, lymphoma and nearly all cases of chronic myelogenous leukemia have a consistent mutated gene (oncogene) that can be identified in the laboratory and aids in the specific classification of the disease. In some cases of leukemia and lymphoma, the oncogene has not been identified. The normal gene is referred to as a proto-oncogene. These genes are usually involved in the regulation of cell growth or survival or the intermediate steps in those processes.

Oncologist: A physician who diagnoses and treats patients with cancer. They are usually internists who treat adults or pediatricians who treat children. Radiation oncologists specialize in the use of radiation to treat cancer and surgical oncologists specialize in the use of surgical procedures to diagnose and treat cancer. These physicians cooperate and collaborate to provide the best treatment plan (surgery, radiation therapy, chemotherapy, or immunotherapy) for the patient.

Opportunistic Infection: The term applied to infections with bacteria, viruses, fungi, or protozoa to which individuals with a normal immune system are not usually susceptible. These organisms take advantage of the opportunity provided by immunodeficiency. Immune deficiency can be acquired as a result of cancers of the lymphatic system such as Chronic Lymphocytic Leukemia or myeloma, can be induced or made more severe in patients who require intensive, prolonged chemotherapy or radiotherapy, can result as a consequence of infection with the human immunodeficiency virus (HIV), and can occur as a sequel to allogeneic stem cell transplantation and severe graft versus host disease.