Glossary

alleles: Different forms of the same gene. A tumor suppressor gene can have alleles that encode proteins that block cell division and cancer, and others that do not.

angiogenesis: Recruitment of a blood supply by a tumor. The tumor sends out a chemical signal to nearby blood vessels, which sprout branches that grow to the tumor.

antibody: A highly specific protein made by the immune system in response to a substance foreign to the body that is involved in immune protection against that substance. Antibodies can be engineered to act as therapeutic agents.

apoptosis: Genetically programmed series of events that results in the death of damaged cells. Cancer chemotherapy often reduces the size of a tumor by increasing apoptosis in tumor cells.

base pairs (nucleotides): Chemical interactions between nucleotides in the same or opposite strands of nucleic acids. A pairs with T or U; G pairs with C.

benign tumor: A tumor that is localized and does not spread to other sites in the body. Benign tumors usually grow to a limited size and are encapsulated by fibrous tissue.

biopsy: Removal of part or all of a tissue suspected of being diseased and laboratory analysis of that tissue to confirm the presence of the disease. Cancer diagnosis is made after biopsy.

cachexia: Bodily state late in cancer where an individual "wastes away," losing appetite and weight. This can occur late in the cancer progression.

cancer stem cells: Cells within a tumor that can form the growing tumor. They may actually be only a small minority of the cells in a particular tumor.

carcinogen: A substance or physical entity that causes damage to a cell, leading to cancer. Most carcinogens are mutagens that damage DNA.

carcinoma: A tumor arising from epithelial cells that are at or near the surface of the body or linings of organs. Because epithelial cells commonly divide, they are quite susceptible to DNA damage and cancer. Most cancers are carcinomas.

case-control study: Epidemiological analysis comparing two populations—one group with a cancer and one group without—and examining the proportion of people exposed to a suspected cancer-causing agent in each group. For example, lung cancer patients versus people without the cancer would be compared for smoking status.

cell: The basic unit of biological structure, function, and continuity. It contains the genome as well as the chemical components for biochemistry.

cell cycle: The sequence of events by which a cell reproduces (divides).

chemoprevention: Use of drugs or nutrients to prevent the development of cancer.

chemotherapy: The use of drugs to treat a disease; used most commonly with cancer and some infectious diseases.

chromosome: A DNA molecule containing all or part of the genome of an organism and has the ability to replicate.

clinical trial: Experimental treatment of a group of patients under carefully controlled conditions to determine the effectiveness of a new treatment.

clone: Genetically identical cells or organisms that arise from a single cell. Although cancers are in general clonal, different cells of a tumor may contain different mutations.

cohort study: Epidemiological analysis comparing two populations—one exposed to a suspected cancer-causing agent and the other not exposed—and examining the proportion of diseased people in each group. For example, smokers and nonsmokers would be compared with respect to lung cancer.

combination chemotherapy: Simultaneous use of several drugs, each directed at a different target to treat a disease. Most cancer chemotherapy uses combinations.

differentiated cell: A cell that has a specialized function, such as muscle. Usually, cells are irreversibly differentiated. Cancer cells are relatively less differentiated or undifferentiated.

DNA: Deoxyribonucleic acid, a polymer of nucleotide building blocks (A, T, G, and C) that acts as the genetic material in most living things.

DNA microarray: A collection of many gene sequences, usually affixed to a glass slide, that acts as a probe for gene expression. Microarrays are being used for cancer diagnosis and prognosis and to monitor treatment.

DNA repair: Chemical correction by cells of errors that occur in DNA during its replication or by outside agents, such as chemicals and radiation. Some cancers are caused in part by defects in DNA repair.

enzyme: A biological catalyst that speeds up a biochemical transformation without emerging changed by the process; most enzymes are proteins, although some are RNAs.

epidemiology: The science of the incidence, course, and determinants of disease in populations. Cancer epidemiology has been useful at pointing to possible causes.

epigenetics: Changes in DNA or its expression that can be passed on to daughter cells but do not basically change the genetic capacities of the nucleotides in DNA. These changes include adding methyl groups of C in DNA or altering the proteins that bind to DNA and occur in many cancers.

eukaryotic cell: A cell with a nucleus and other cell components that are each enclosed within membranes; these cells make up animals (including humans) and plants.

gene: The unit of heredity; a sequence of nucleotides on a chromosome that is expressed as a product that is part of the phenotype.

genetic code: The sequence of nucleotides along mRNA that is used to translate the genome into amino acids in protein. The code is virtually the same in all organisms.

gene therapy: Addition of a natural or artificially made gene to a tumor to therapeutically alter its properties.

genome: A complete genetic sequence of an organism or cell. The Cancer Genome Anatomy Project seeks to describe the genomes of tumor types.

growth factor: A protein made in mammals by one tissue that stimulates cell division in a target tissue.

hereditary cancer: Cancer that develops because of gene mutation(s) passed on from parent to offspring.

heterozygote: An organism with two different alleles for a particular gene.

homozygote: An organism with two identical alleles for a particular gene.

immune system: Body functions that recognize and defend against substances foreign to the body, most notably infectious diseases. The immune system often recognizes cancer cells as foreign due to their genetic changes and kills the tumor.

incidence: Frequency of a disease in a population per unit of time. For cancer, incidence is typically expressed as the number of new cases per 100,000 per year.

induced mutation: Inherited DNA change caused by an external agent, such as a chemical or radiation. If this occurs in an oncogene or a tumor suppressor gene, it can contribute to the development of cancer. Many carcinogens cause induced mutations.

leukemia and lymphoma: Cancers of the white blood cell system, usually arising from immature, not fully differentiated cells.

loss of heterozygosity: Occurs when both copies of a tumor suppressor gene are mutated, so that there is not a normally functioning allele. As a result, cell division is permitted, and cancer can result.

lymph node: Accumulated tissue in the tubes of the lymphatic system that drains fluids in between tissues and returns it to the blood system. Because tumor metastasis often occurs via lymphatic vessels, tumor cells can accumulate in lymph nodes, and detection of them there indicates metastasis or its potential.

malignant tumor: A tumor that spreads from its site of origin to other sites in the body. The tumor spreads by cells migrating to the blood or lymphatic systems.

metabolism: The sum total of all of the chemical transformations in an organism.

metastasis: The ability of a tumor to break off cells, which travel in the blood or lymphatic system to a new location in the body and grow to a satellite tumor.

mitosis: Division of the nucleus of a cell, separating two replicated sets of chromosomes. The presence of a large number of cells in mitosis is a hallmark of aggressive cancers.

multidrug resistance: Development of resistance in a tumor to previously effective drugs.

multistep model: Series of sequential events describing the development of a tumor—from initial damage of a cell to tumor metastasis. Each event is mediated by distinctive genetic and cellular changes.

mutagen: A substance that damages DNA, leading to permanent genetic changes in the effected cell and its descendants. Most cancer-causing entities in the environment are mutagens.

mutation: A change in the genetic material that is passed on to both daughter cells after cell division. If the cell is a germ line cell, then the change can be passed on to offspring and is inherited. If the change is in a somatic cell, then it is passed on only to the cells deriving from the original changed cell.

nucleic acid: A large molecule of DNA or RNA made up of nucleotide building blocks.

nucleotide: The building block of a nucleic acid. Each nucleotide has an identical sugar and phosphate group, but there is one of five different bases: A, G, C, T, and U.

oncogene: A gene carried by a virus that, when activated, forms a product that acts as a "gas pedal" to stimulate cell division, leading to cancer. Some oncogenes form growth factors; others form receptors for growth stimulators. Still others form molecules that block cell death.

oncology: The study of cancer as a disease. A medical oncologist is a physician who treats cancer, usually with medications. A radiation oncologist uses radioactivity, and a surgical oncologist uses surgery.

pharmacology: The scientific study of drugs and their interactions with the body (as opposed to pharmacy, which is the formulation and dispensing of drugs). Pharmacology includes pharmacokinetics, describing events occurring before a drug enters a targeted cell, and pharmacodynamics, describing events occurring after a drug reaches a targeted cell. Both must be fully understood for the development of effective cancer-fighting drugs.

phases I, II, and III: In clinical trials for new therapies, the sequence of protocols needed before a drug or other modality is approved for use as standard care. In phase I, patients with the disease are given the therapy to determine toxicity and tolerability of the dose. In phase II, a small number of patients are given treatment while others are given no treatment, and effectiveness and side effects are evaluated and compared. In phase III, a large number of patients are given treatment or no treatment, and the results are compared.

phenotype: The outward appearance resulting from the expression of a gene. It can be influenced by the environment.

polymerase chain reaction (PCR): A method of amplifying a DNA sequence in a test tube by adding DNA polymerase and other necessary components for replication. A sequence can be amplified a million times in a few hours.

progression: Growth of a tumor from a baseline size. Various definitions are used to measure tumor size. Progression is used as an endpoint in some clinical trials.

promoter: A DNA sequence adjacent to the coding region of a gene, to which RNA polymerase binds to initiate gene expression. The events at the promoter are highly regulated in location and time. Prompters regulate the expression of genes involved with cancer.

prophylactic surgery: Prevention of cancer development in individuals at risk by surgical removal of tissues that might become cancerous. For example, in women carrying mutations that make them susceptible to breast cancer, the breasts are removed before cancer has a chance to develop.

protein: A large molecule composed of amino acid building blocks linked together.

proto-oncogene: A gene in a cell that, when activated, forms a product that stimulates cell division and cancer. Homologous to oncogenes carried by viruses.

radiation therapy: The use of radiation-emitting isotopes of chemical elements to treat cancer. Radiation is typically given in small doses over several weeks to avoid extensive damage to normal tissues.

recessive: An allele that is expressed only when homozygous and not expressed when heterozygous (the dominant allele is expressed).

restriction point: Stage of the cell division cycle when a "decision" is made to proceed and replicate DNA, setting the stage for division. There is extensive regulation at this point, and cancer cells often lack proper regulation, leading to continuous cell reproduction.

risk analysis: Evaluation of both biological and social aspects of an activity in relation to disease. In cancer, risk analysis involves a quantitative estimation of the hazard of exposure to a carcinogen and cost-benefit analysis of its value to the individual.

risk factor: Genetic or environmental condition that makes it more likely that an individual will get a disease. In cancer, there are causative risk factors (if removed, a person does not get cancer) and descriptive risk factors (put people at risk but are not causes).

RNA: Ribonucleic acid, a polymer of the nucleotides A, G, C, and U. There are several types of RNA in the cell, such as transfer RNA and messenger RNA. They are mostly involved in gene expression.

sarcoma: A tumor originating in tissues, such as muscle, below the surface of the body or lining of organs.

screening: The use of a relatively simple test to identify people who probably have a disease. For example, a mammogram is an X-ray of breast tissue that identifies growths that could be cancer. Diagnosis is made after biopsy.

semiconservative replication: The mechanism of duplication of DNA whereby each of the two strands in the parental DNA acts as a template for a new strand by complementary base pairing so that each of the two DNA molecules produced has one parental and one new strand.

somatic mutation: Permanent DNA change in a cell that does not participate in sexual reproduction. Most cancers involve somatic mutations.

spontaneous mutation: Permanent, inherited change in DNA caused by the internal chemistry of the cell, commonly due to errors in DNA replication. Cancers without a known cause probably develop by spontaneous mutation.

sporadic cancer: Cancer occurs without a known hereditary cause.

stem cells: Continuously dividing, undifferentiated cells in the body that replace cells that are lost due to wear and tear or programmed cell death. Cancers can develop from stem cells.

stem cell transplantation: Replacement of bone marrow stem cells destroyed by cancer chemotherapy or radiation. The new cells may be either from the treated individual (stored previously) or from a donor whose cells are genetically similar to the recipient.

targeted chemotherapy: Use of a drug that has a rather specific target molecule in a diseased cell. This is done to minimize side effects of treatment. It is a frontier of cancer treatment.

telomere: The two ends of a chromosome, where specific DNA sequences prevent DNA damage when it replicates.

teratoma: Rare cancer in which there are multiple differentiation events within the tumor. For example, a teratoma in the abdomen may contain fragments of bone and kidney.

therapeutic index: A mathematical comparison between damage done to cancer cells and to normal body cells at a given dose of therapeutic agent. The wider the therapeutic ratio, the more effective the treatment. A major goal of cancer treatment is to widen the therapeutic ratio.

transcription: The expression of a gene by the production of RNA from a DNA template, catalyzed by RNA polymerase.

transformation: In cancer, the conversion of a normal cell into a cancer cell. in experimental science, the introduction of DNA from an outside source to cell, causing it to become genetically different.

translation: The synthesis of a chain of amino acids as a protein in response .0 the information of a nucleotide sequence in a gene as appearing in mRNA.

translocation: Transfer of part of one chromosome onto another. This shuffling of genes usually results in alteration of gene expression and cell function. Translocations are common in blood cancers and solid tumors.

tumor grade: Seen on biopsy, the fraction of cancer cells that are either dividing and do not resemble the cells of origin (high-grade tumor) or are not dividing and resemble the cells of origin (low-grade tumor). High-grade tumors have a worse prognosis than low-grade tumors.

tumor marker: A substance either in a tumor cell or released by it to the blood that signals the presence of a tumor to a physician when it is identified. Tumor markers can be used in diagnosis or to monitor treatment.

tumor stage: A graded series of evaluations at diagnosis of how far the tumor has invaded its organ of origin. Higher-stage tumors generally have a worse prognosis than lower-stage tumors on the surface of an organ.

tumor suppressor gene: A gene in a cell whose product normally inhibits cell division, leading to cancer. Some tumor suppressor genes form molecules that inhibit progress through the cell division cycle, and others form molecules that are involved in the repair of DNA damage.

vaccine: A harmless formulation of a disease agent foreign to the body that provokes an immune response that protects the body from infection by the intact disease agent. Vaccines against certain viruses that cause cancer can be used to prevent those cancers. Vaccines can also be made against tumors after they develop.