Acute lymphoblastic leukemia: a variant of white blood cell cancer that affects the lymphoid lineage of blood cells.

Acute myeloid leukemia: a variant of white blood cell cancer that affects the myeloid lineage of blood cells.

Apoptosis: the regulated process of cell death that occurs in most cells, involving specific cascades of genes and proteins.

Carcinogen: a cancer-causing or cancer-inciting agent.

Chimeric gene: A gene created by the mixing together of two genes. A chimeric gene might be the product of a natural translocation, or might be engineered in the lab.

Chromosome: a structure within a cell comprised of DNA and proteins that stores genetic information.

Cytotoxic: Cell-killing. Usually refers to chemotherapy that works by killing cells, particularly rapidly dividing cells.

DNA: Deoxyribonucleic acid, a chemical that carries genetic information in all cellular organisms. It is usually present in the cell as two paired, complementary strands. Each strand is a chemical chain made up of four chemical units—abbreviated A, C, T, and G. Genes are carried in the form of a genetic “code” in the strand and the sequence is converted (transcribed) into RNA (see p. 534) and then translated into proteins (see p.534).

Enzyme: a protein that accelerates a biochemical reaction.

Gene: a unit of inheritance, normally comprised of a stretch of DNA that codes for a protein or for an RNA chain (in special cases, genes might be carried in the RNA form).

Genetic engineering: the capacity to manipulate genes in organisms to create new genes, or introduce genes into heterologous organisms (e.g., a human gene in a bacterial cell).

Genome: the full complement of all genes within the organism.

Incidence: In epidemiology, the number (or fraction) of patients who are diagnosed with a disease in a given period of time. It differs from prevalence because incidence reflects the rate of new diagnosis.

Kinase: a protein enzyme that attaches phosphate groups to other proteins.

Metastatic: cancer that has spread beyond its local site of origin.

Mitosis: the division of one cell to form two cells that occurs in most adult tissues of the body (as opposed to meiosis, which generates germ cells in the ovary and the testes).

Mutation: An alteration in the chemical structure of DNA. Mutations can be silent—i.e., the change might not affect any function of the organism—or can result in a change in the function or structure of an organism.

Neoplasm, neoplasia: an alternative name for cancer.

Oncogene: A cancer-causing or cancer-promoting gene. Activation or overexpression of a proto-oncogene (see below) promotes the transformation of a cell from normal to a cancer cell.

Prevalence: in epidemiology, the number (or fraction) of affected patients in any given period of time.

Primary prevention: prevention aimed at avoiding the development of a disease, typically by attacking the cause of the disease.

Prospective trial: a trial in which a cohort of patients is followed forward in time (as opposed to retrospective, in which a cohort of patients is followed backward).

Protein: A chemical comprised, at its core, of a chain of amino acids that is created when a gene is translated. Proteins carry out the bulk of cellular functions, including relaying signals, providing structural support, and accelerating biochemical reactions. Genes usually “work” by providing the blueprint for proteins (see DNA, p. 533). Proteins can be modified chemically by the addition of small chemicals such as phosphates or sugars or lipids.

Proto-oncogene: A precursor to an oncogene. Typically, proto-oncogenes are normal cellular genes that, when activated by mutation or overexpression, promote cancer. Proto-oncogenes typically code for proteins that are associated with cell growth and differentiation. Examples of proto-oncogenes include ras and myc.

Randomized trial: a trial in which treatment and control groups are randomly assigned.

Retrovirus: an RNA virus that keeps its genes in the form of RNA and is capable, by virtue of an enzyme, reverse transcriptase, to convert its genes from the RNA form into a DNA form.

Reverse transcriptase: An enzyme that converts a chain of RNA into a chain of DNA. Reverse transcription is a property of retroviruses.

RNA: Ribonucleic acid, a chemical that performs several functions in the cells, including acting as an “intermediate” message for a gene to become a protein. Certain viruses also use RNA, not DNA, to maintain their genes (see Retrovirus, above).

Secondary prevention: Prevention strategies that are aimed at early detection of a disease, typically by screening asymptomatic men and women. Typically, secondary prevention strategies attack early, pre-symptomatic stages of the disease.

Transfection: the introduction of DNA into a cell.

Transgenic mice: mice in which a genetic change has been artificially introduced.

Translocation (of a gene): the physical reattachment of a gene from one chromosome to another.

Tumor suppressor gene (also called anti-oncogene): A gene that, when inactivated fully, promotes the progression of a cell into a cancer cell. Tumor suppressors usually protect a cell from one step on the progression toward cancer. When this gene is mutated to cause a loss or reduction in its function, the cell can progress to cancer. Typically, this occurs in combination with other genetic changes.

Two-hit hypothesis: the notion that for tumor suppressor genes, both functionally intact copies of the gene must be inactivated in order for a cell to progress toward cancer.

Virus: A microorganism that is incapable of reproducing by itself, but capable of creating progeny once it has infected a cell. Viruses come in diverse forms, including DNA viruses and RNA viruses. Viruses possess a core of either DNA or RNA, coated with proteins, and can be bound by an outer membrane made of lipids and proteins.

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