Cancer Genetics

Prevention and Treatment: Glossary of Terms

BRCA1/BRCA2: The first breast cancer genes to be identified. Mutated forms of these genes are believed to be responsible for about half the cases of inherited breast cancer, especially those that occur in younger women. Both are tumor suppressor genes. Individuals with mutations in BRCA1/BRCA2 have hereditary breast and ovarian cancer syndrome.

Cancer: Diseases in which abnormal cells divide and grow unchecked. Cancer can spread from its original site to other parts of the body and can also be fatal if not treated adequately.

Cell: The basic unit of any living organism. It is a small, watery, compartment filled with chemicals and a complete copy of the organism's genome.

Chromosome: One of the threadlike "packages" of genes and other DNA in the nucleus of a cell. Different kinds of organisms have different numbers of chromosomes. Humans have 23 pairs of chromosomes, 46 in all. Each parent contributes one chromosome to each pair, so children get half of their chromosomes from their mothers and half from their fathers.

DNA (deoxyribonucleic acid): the chemical inside the nucleus of a cell that carries the genetic instructions for making living organisms.

Gene: The functional and physical unit of heredity passed from parent to offspring. Genes are pieces of DNA, and most genes contain the information for making a specific protein.

Genetic counseling: An educational counseling process for individuals and families who have a genetic disease or who are at risk for such a disease. Genetic counseling provides patients with information about the suspected condition and helps them understand and adapt to the medical, psychological and familial implications of genetic contributions to disease. This process integrates the following:

  • Interpretation of family and medical histories to assess the chance of disease occurrence or recurrence.
  • Education about inheritance, testing, management, prevention, resources and research.
  • Counseling to promote informed choices and adaptation to the risk or condition.

Genetic Counselor: A specially trained health care professional who assesses genetic risk and educates patients about these risks, genetic testing and healthcare management, screening, and prevention options. A Genetic Counselor has a specialized graduate degree and board certification in genetic counseling.

Genome: All of the DNA contained in an organism or a cell

HNPCC: Hereditary Non-Polyposis Colorectal Cancer, also known as Lynch syndrome. This is the most common form of hereditary colorectal cancer and accounts for approximately 5% of all colorectal cancers. Other types of cancer seen in families with HNPCC are endometrial, stomach, ovarian, small bowel, urinary tract, liver and bile duct cancers.

Mutation: A permanent structural alteration in DNA. DNA changes either have no effect, cause harm, or occasionally cause improvement.

Nucleus: The central cell structure that houses the chromosomes.

Tumor suppressor gene: A protective gene that normally limits the growth of tumors. When a tumor suppressor is mutated, it may fail to keep a cancer from growing.

Additional genetic terms and definitions can be found at the National Human Genome Research Institute website at