E

E. coli: Common bacterium that has been studied intensively by geneticists because of its small genome size, normal lack of pathogenicity, and ease of growth in the laboratory.

Edema: Fluid build-up in tissue, causing swelling. Can occur in the arm after radical mastectomy, dissection of lymph nodes, or radiation. (See: Lymphedema.) 

Electrofulguration: Treatment that destroys cancer cells by burning with electrical current.

Electrophoresis: Method of separating large molecules (such as DNA fragments or proteins) from a mixture of similar molecules. An electric current is passed through a medium containing the mixture, and each kind of molecule travels through the medium at a different rate, depending on its electrical charge and size. Separation is based on these differences. Agarose and acrylamide gels are the media commonly used for electrophoresis of proteins and nucleic acids.

Embolization: The process of blocking or clogging a blood vessel: A treatment that reduces blood supply to cancer by injection of materials to plug up the blood vessels that supply blood (and nutrients) to the tumor. 
Emesis: Vomiting. 

Endocrine glands: Glands that release hormones into the blood. Ovaries are a type of endocrine gland. 

Endocrine therapy: Manipulating hormones to treat a disease or condition. (See: Hormone therapy.) 

Endocrinologist: Physician specializing in diseases related to the glands of the endocrine system, such as the thyroid, pancreas, and adrenal glands. 

Endometrium: Lining of the womb (uterus). 

Endonuclease: An enzyme that cleaves its nucleic acid substrate at internal sites in the nucleotide sequence.

Endoscopy: Inspection of organs or body cavities using a flexible, lighted tube (endoscope).

Enterostomal therapist: Health professional who teaches people how to care for ostomies (surgically created openings such as a colostomy) and other wounds.Enzyme: A protein that acts as a catalyst, speeding the rate at which a biochemical reaction proceeds but not altering the direction or nature of the reaction.

Enzyme: Protein that acts as a catalyst to speed the rate at which a biochemical reaction proceeds but not altering the direction or nature of the reaction. 

Epidemiology: Study of diseases in populations by collection/analysis of statistical data. In the field of cancer, for instance, epidemiologists study how many people have cancer; who gets specific types of cancer; and what factors (such as environment, job hazards, family patterns, and personal habits, such as smoking and diet) play a part in cancer development.

Esophageal speech: Speech system used by some people after cancer surgery on the voice box (larynx). Air is swallowed and a "belching" type of speech can be produced. New devices, improved surgery, and use of chemotherapy and radiation instead of surgery, have reduced the need for learning esophageal speech.

EST: Expressed sequence tag. See sequenced tagged site.

Estrogen: Female sex hormone produced primarily by the ovaries. Adrenal cortex also produces small amount. In women, estrogen levels fluctuate on a schedule. Estrogen regulates development of secondary sex characteristics, including breasts; regulates the monthly menstruation cycle; and prepares the body for fertilization and reproduction. In breast cancer, estrogen may promote growth of cancer cells. (See Estrogen receptor assay, Estrogen replacement therapy.) 

Estrogen receptor assay : A lab test done on a cancer sample to see whether estrogen receptors are present. The growth of normal breast cells and some breast cancers is stimulated by estrogen. Estrogen receptors are molecules that function as a cells' "welcome mat" for estrogen circulating in the blood. Breast cancer cells without these receptors (called estrogen receptor negative or ER negative) are unlikely to respond to hormone treatments. ER positive cancers are more likely to respond. 

Etiology: The cause of a disease.

Eukaryote: Cell or organism with membranebound, structurally discrete nucleus and other welldeveloped subcellular compartments. Eukaryotes include all organisms except viruses, bacteria, and bluegreen algae. Compare prokaryote. See chromosome.

Evolutionarily conserved: See conserved sequence.

Exogenous DNA: DNA originating outside an organism.

Extended radical mastectomy: Removal of the breast, skin, nipple, areola, chest muscles (pectoral major and minor), and all axillary and internal mammary lymph nodes on the same side.

Exon: The proteincoding DNA sequence of a gene. Compare intron.

Exonuclease: An enzyme that cleaves nucleotides sequentially from free ends of a linear nucleic acid substrate.

Expressed gene: See gene expression.