A

Ablative therapy: Treatment that removes or destroys the function of an organ, for example, removing the ovaries or testicles or having some types of chemotherapy that cause them to stop working. 

Adenocarcinoma: A type of cancer that starts in the glandular tissue, such as in the ducts or lobules of the breast. 
Adenoma: Benign growth starting in the glandular tissue. 

Adenomatous polyps: Benign growths of glandular cells, for example, those that line the inside of the colon or rectum. There are three types of colorectal adenomas: tubular, villous, and tuberovillous 

Adenomatous polyps or adenoma: Benign growth of glandular cells, for example, those that line the inside of the colon or rectum. There are three types of colorectal adenomas: tubular, villous, and tuberovillous. Adenine (A): A nitrogenous base, one member of the base pair AT (adeninethymine).

Adjuvant therapy : Treatment used in addition to the main treatment. It usually refers to hormonal therapy, chemotherapy, radiation therapy, or immunotherapy added after surgery to increase the chances of curing the disease or keeping it in check. 

Adrenal gland : One adrenal gland is located near each kidney. Their main function is to produce hormones which control metabolism, fluid balance, and blood pressure. In addition, they produce small amounts of "male" hormones (androgens) and "female" hormones (estrogens and progesterone). 

Advance directives : Legally binding documents that tell doctors and family what a person wants for future medical care, including whether to start or when to stop life-sustaining treatment. 
Allele: Alternative form of a genetic locus; a single allele for each locus is inherited separately from each parent (e.g., at a locus for eye color the allele might result in blue or brown eyes).

Alopecia: Hair loss. This often occurs as a result of chemotherapy or from radiation therapy to the head. In most cases, the hair grows back after treatment ends. 

Alternative therapy : Use of unproven therapy instead of standard (proven) therapy. Some alternative therapies have dangerous or even life-threatening side effects. With others, the main danger is that the patient may lose the opportunity to benefit from standard therapy. patients considering alternative or "complementary" therapy should discuss it with their health care team. (See: complementary therapy).

Alveoli: Air cells of the lungs.

Amino acid: Any of a class of 20 molecules that are combined to form proteins in living things. The sequence of amino acids in a protein and hence protein function are determined by the genetic code.
Amplification: An increase in the number of copies of a specific DNA fragment; can be in vivo or in vitro. See cloning, polymerase chain reaction

Androgen: Any male sex hormone. (Testosterone is the major androgen.) 

Androgen blockade: Use of drugs to disrupt actions of male hormones. 

Anemia: Low red blood cell count. 

Anesthesia: Loss of feeling or sensation as a result of drugs or gases. General anesthesia causes loss of consciousness ("puts you to sleep"). Local or regional anesthesia numbs only a certain area. 

Anesthesiologist: Doctor specializing in giving medicines or other agents that prevent or relieve pain, especially during surgery. 

Aneuploid: (See ploidy.) 

Angiogenesis: Formation of new blood vessels. Some cancer treatments work by blocking angiogenesis, preventing blood from reaching the tumor. 

Antibiotics: Drugs used to kill organisms that cause disease. Because some cancer treatments reduce the body's ability to fight infection, antibiotics may be used to treat or prevent infection. 

Antibody: Antibodies defend against foreign agents, such as bacteria. Antibodies are proteins produced by immune system cells, which then release them into the blood. (See: antigen). 

Antiemetic: Drug that prevents/relieves nausea and vomiting - often common side effects of chemotherapy. 

Antiestrogen: Substance (drug) that blocks the effects of estrogen on tumors. Antiestrogens are commonly used to treat breast cancer, which depends on estrogen for growth. 

Antigen: Substance that causes the immune system to react - often involving production of antibodies. For example, antigens that are part of bacteria and viruses cause the immune system to respond and helps protect people from infection. Cancer cells also have certain antigens that can be found by lab tests. These antigens are important in cancer diagnosis and in gauging response to treatment. Other cancer antigens may even trigger the body's own cancer-fighting agents.. 

Antimetabolites: Substances that interfere with the body's chemical processes, such as those creating proteins, DNA, and other chemicals needed for healthy cell growth and cell reproduction. In treating cancer, antimetabolite drugs disrupt DNA production, which, in turn, prevents cell division and growth of tumors. (See: DNA.) 

Antioxidants: Compounds that stop or retard chemical reactions with oxygen (oxidation) and are thought to reduce the risk of some cancers. Vitamins C and E and beta-carotene are some common antioxidants.

Antisense - Antisense drugs work at the genetic level to interrupt the process by which disease-causing proteins are produced. Proteins play a central role in virtually every aspect of human metabolism. Almost all human diseases are the result of inappropriate protein production (or disordered protein performance). This is true of both host diseases (such as cancer) and infectious diseases (such as AIDS). Traditional drugs are designed to interact with protein molecules throughout the body that support or cause diseases. Antisense drugs are designed to inhibit the production of disease-causing proteins. They can be designed to treat a wide range of diseases including infectious, inflammatory and cardiovascular diseases and cancer and have the potential to be more selective and, as a result, more effective and less toxic than traditional drugs.

Apoptosis: Programmed cell death controlled by genes that cause a cell to die at a specific time. Apoptosis can be brought about by some drugs used to treat cancer.

Arrayed library: Individual primary recombinant clones (hosted in phage, cosmid, YAC, or other vector) that are placed in two-dimensional arrays in microtiter dishes. Each primary clone can be identified by the identity of the plate and the clone location (row and column) on that plate. Arrayed libraries of clones can be used for many applications, including screening for a specific gene or genomic region of interest as well as for physical mapping. Information gathered on individual clones from various genetic linkage and physical map analyses is entered into a relational database and used to construct physical and genetic linkage maps simultaneously; clone identifiers serve to interrelate the multilevel maps. Compare library, genomic library.

Aspiration: To draw out by suction.

Asymptomatic: Having no symptoms of disease. Many cancers can develop and grow without producing symptoms, especially in the early stages. Tests - such as mammograms - help find these cancers when chances for cure are highest.

Atypical: Not usual. Often refers to appearance of cancerous or precancerous cells. (See: hyperplasia.) 

Autologous bone marrow transplantation: See bone marrow transplantation. 

Autoradiography: A technique that uses X-ray film to visualize radioactively labeled molecules or fragments of molecules; used in analyzing length and number of DNA fragments after they are separated by gel electrophoresis.

Autosome: A chromosome not involved in sex determination. The diploid human genome consists of 46 chromosomes, 22 pairs of autosomes, and 1 pair of sex chromosomes (the X and Y chromosomes).

Axilla: Armpit.

Axillary dissection: Removal of the lymph nodes in the armpit (axillary nodes). They are examined for the presence of cancer.