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Quality of Life: The overall enjoyment of life. Many clinical trials assess the effects of cancer and its treatment on the quality of life. These studies measure aspects of an individual's sense of well-being and ability to carry out various tasks.

RNA (Ribonucleic Acid): There are several types of RNA. Messenger RNA is a copy of a stretch of DNA, a gene, that is transcribed into RNA, which is used by cells as a template for making a protein from individual amino acids. A second form of RNA, transfer RNA, carries the amino acid to the site at which it combines with other amino acids to make the complete protein.

Radioactive Isotope: A form of a molecule that emits radiation. There are three principal type of isotope emitters: alpha, beta, and gamma. Isotopes can be used as diagnostic agents in nuclear medicine. Such agents are chosen because they have an affinity for certain organs or tissues. One can use instruments to detect these isotopes. Brain, bone, liver, and spleen scans are examples of use of isotopes for diagnosis of abnormalities of those organs. Certain radioactive isotopes can damage cancer cells. Physicians use radioactive isotopes to treat cancer in several ways, including attaching the isotope to antibodies made against cancer cell antigens. The antibodies can attach to the cancer cell and the radiation can destroy it and neighboring cells.

Radiotherapy: The use of x-rays and other forms of radiation in treatment. Radiotherapy is useful in the treatment of localized lymphomas, especially Hodgkin lymphoma, central nervous system lymphoblastic leukemia, and localized myeloma.

Recombinant: A term used to describe drugs that have been produced using the techniques of genetic engineering. The products are virtual replicas of compounds produced naturally by the body.

Red Cells: Blood cells that contain hemoglobin. Hemoglobin binds oxygen when red cells pass through the lung and releases it to the tissues of the body. The red cells make up a little less than half the volume of blood in healthy individuals.

Reed-Sternberg Cell: The malignant T-cell in Hodgkin lymphoma. It takes various forms but is classically a large cell with two nuclei that is derived from a B-Lymphocyte. Thus, Hodgkin disease is now classified as a B-cell lymphoma.

Refractory Anemia: A clonal myeloid disorder that primarily affects red cell production in the marrow. In some cases the developing red cells have an abnormal accumulation of iron granules around the nucleus. These cells are called ringed sideroblasts. Refractory anemia (RA) and refractory anemia with ringed sideroblasts (RARS) are often associated with mild to moderate decreases in white cells and platelets. These disorders are also referred to as myelodysplasia.

Refractory Anemia with Excess Blasts: A clonal myeloid disorder characterized by the marrow and blood features of refractory anemia but with overt leukemic myeloblasts evident in the marrow and sometimes the blood. Usually the marrow blast T-cell proportion is between two and twenty percent. The disorder is also referred to as oligoblastic (low blast count) leukemia. The disease is less rapidly progressive than florid acute myelogenous leukemia but often evolves into an such a more acute leukemia.

Relapse or Recurrence: A return of the disease after it has been in remission following treatment.

Relative Survival Rate: An estimate of the percentage of patients that would be expected to survive the effects of their disease. This rate is calculated by adjusting the observed survival rate so that the effects of causes of death, other than those related to the disease in question, is removed. (Observed survival is the actual percentage of patients still alive at some specified time after diagnosis of disease. It considers deaths from all causes.)

Remission: A disappearance of evidence of a disease, usually as a result of treatment. The terms “complete” or “partial” are used to modify the term “remission.” Complete remission means all evidence of the disease is gone. Partial remission means the disease is markedly improved by treatment, but residual evidence of the disease is present. Long-term benefit usually requires a complete remission, especially in acute leukemia or progressive lymphomas.

Remission Induction Therapy: The initial course of treatment given to patients on admission to hospital, which is intended to remove all evidence of clinically detectable leukemia or lymphoma.

Resistance to Treatment: The ability of cells to live and divide despite their exposure to a chemical that ordinarily kills cells or inhibits their growth. Refractory leukemia, lymphoma, or myeloma is the circumstance in which a proportion of malignant T-cells resist the damaging effects of a drug or drugs. Cells have several ways to develop drug resistance. (See Multi-drug Resistance)

Reticulocyte: The red cell for several days after it loses its nucleus in the marrow and for the first day of its life span in the blood contains leftover material that can be stained. In this way, the proportion of cells that are newly delivered into the blood from the marrow can be identified. Normally, a low proportion of reticulocytes (about 1% of red cells) are present in the blood. An increase in numbers indicates an increased production in the marrow, for example following blood loss, to replace lost blood cells.

Retinoic Acid: A synthetic form of vitamin A, which can stimulate promyelocytic leukemia cells to mature. It is used in combination with chemotherapy to treat acute promyelocytic leukemia.

Retinoic Acid Receptor Alpha Gene (RAR-α): The gene for the retinoic acid receptor that is disrupted in the translocation between chromosome 15 and 17 in acute promyelocytic leukemia.

Retrovirus: A family of viruses composed of RNA. Once in a host T-cell they can use reverse transcriptase to perform a “backwards” conversion of RNA to DNA. This family of viruses can cause leukemia in animals. Three forms have been associated with human disease. The two most important are the human immunodeficiency virus, which causes AIDS, and the human T-lymphocytotropic virus 1, which causes an acute lymphoblastic leukemia/lymphoma syndrome in adults in certain geographic areas.

Risk Factor: A factor that is scientifically established to increase a person's chance of getting a disease. Risk factors can be classified as either genetic (inherited), lifestyle-related, or environmental. The presence of one or more risk factors does not mean that a person will necessarily develop the disease. In the case of environmental exposure, extent of exposure and duration are important considerations in determining if risk is increased.

Rituxan (Rituximab): is the first monoclonal antibody found to be effective and safe for the treatment of cancer in the United States. Rituxan is indicated for treatment of patients with relapse or refractory, low-grade or follicular, CD20-positive, B-cell non-Hodgkin's lymphoma (NHL) which is a cancer of the lymphatic system.