Kenneth Offit, Chief of Memorial Sloan-Kettering's Clinical Genetics Service, discusses which tests should be used — or avoided — to guide your efforts to act on your familial risk for cancer of the colon or breast.
Everyone has some risk of developing cancer, and in most cases the disease develops by chance. However, some people are genetically predisposed to developing certain types of cancer. These people have a higher risk of developing the disease than those in the general public.
DNA is present in almost every cell in our body and carries the basic instructions our cells and tissues need to function properly. DNA is packaged into structures called chromosomes. Most people’s cells contain 23 different chromosomes that come in two identical sets — one set from our mother, and one from our father — or 46 chromosomes in total.
Scattered across our chromosomes are approximately 25,000 genes, which are functional units of DNA. The cell uses genes to make proteins and other substances that are necessary for life. In some genes, changes in the DNA called mutations have been linked to cancer.
Genes and Cancer
Cancer is usually caused by gene mutations that occur randomly in one or a few cells of the body. Such gene changes, called somatic mutations, may arise as a natural consequence of aging or when a cell’s DNA has been damaged. Acquired mutations are only present in some of the body’s cells, and they are not passed on from parents to their children.
However, in a small percentage of people with cancer, the disease is due to a different type of mutation called a hereditary mutation, or germline mutation. These mutations are usually inherited from one or both of the person's parents, and are present in nearly every cell of the body. Because hereditary mutations are present in the DNA of sperm and egg cells, they can be passed down in families.
People who carry such hereditary mutations do not necessarily get cancer, but their risk of developing the disease at some point during their lifetime is higher than average.
In recent years, scientists have discovered a number of mutations that can contribute to a person’s risk of developing certain cancers, including breast, ovarian, colorectal, and prostate cancer, as well as some other, less common cancer types.
Genetic testing is now available for some hereditary cancers. If you have a family history of cancer, or if you would like to find out whether you or a family member has an increased likelihood of developing cancer, we encourage you to consult with a specialist who has experience in the area of hereditary cancer, cancer risk assessment, and genetic counseling and testing.
Genetic Counseling and Testing
Genetic counseling involves a discussion of your personal or family history of cancer. It is typically recommended for individuals or families with multiple cases of cancer diagnosed at unusually young ages.
Genetic counselors will tell you about the scientific concepts that relate to genetic testing and help you decide what genetic tests, if any, might be useful for you.
Genetic testing involves a simple blood test and may be used to obtain a more precise estimate of your cancer risk. In some cases, genetic testing can be done on stored tissue samples from deceased relatives.
Genetic testing is not required for a cancer risk assessment. However, it may in some cases help you and your physician make important decisions about your medical care.
Deciding whether to undergo genetic testing is a personal choice that can be made at the time of the counseling session or at a future date. Genetic counseling does not require genetic testing, and genetic testing may not be useful for everyone receiving genetic counseling.