Cancer accounts for about 20% of all deaths in the United States. Cancer genetics refers to the medical field that looks at the underlying genetic altgerations of specific cancers, and the ethical, legal, social, and psychological implications of this knowledge.

Genetic information, including information from family history and from DNA-based testing, provides a means to identify people who have an increased risk of cancer.

In some cases, DNA-based testing can be used to confirm a specific mutation as the cause of the inherited risk, and to determine whether family members have inherited the mutation.

Identifying a person with an increased risk of cancer has the purpose of improving that person's health outcome or quality of life, through clinical management strategies to reduce risk or through intrinsic benefits of the information itself. Intrinsic benefits may include better informed decisions about reproduction, retirement, and other life decisions. Methods of genetic risk assessment include empiric models, assessment of family history and genetic testing. Genetic testing is generally undertaken only when family history or other clinical characteristics, such as early onset of cancer, indicate a substantial likelihood of an inherited predisposition to cancer.

Genetic testing may also be sought by people affected with cancer, both newly diagnosed individuals and survivors of earlier cancers. Testing may be desired to identify the cause of the cancer, to clarify risk to offspring, to define the appropriateness of particular surveillance approaches, or to aid in decision-making about risk-reducing preventive surgery. While there are not, as yet, proven effective treatments specific to most cancer genetic syndromes, some patients and physicians may wish to include genetic risk status as a factor in consideration of treatment options.