Cancer Genetics
All cancer can be considered genetic because cancer is the result of multiple errors (mutations) in the genes of a cell. Cancer occurs when a cell has built up enough genetic errors to allow uncontrolled growth and the ability to spread to other parts of the body. (This is a long process that usually takes many years.) For most cancers, all of the genetic errors occur after a person is born. They are the result of aging and/or environmental exposures. Mutations build up in cells over time in much the same way that errors can be introduced into a long report that has been retyped many times.
A small percentage of cancer is related to major cancer predisposition genes. In this situation, certain genes have errors that are inherited, passed on from parent to child. There is much ongoing research in this area. Some of the cancer predisposition genes that have been identified are those relating to breast and ovarian cancer, colon cancer, prostate cancer, and medullary thyroid cancer. It is estimated that about 5% of breast and colon cancers are related to genes with inherited errors.
Families who carry cancer predisposition genes are more likely to have certain characteristics. Usually there are several people in the family (in more than one generation) who have similar or related cancers. Cancer in these families often occurs at an earlier age than average, frequently when people are in their 30's or 40's. Carriers of predisposition genes are more likely to have two separate cancers, for example, both breast and ovarian cancer or cancer in both breasts.
How common is it to have several family members with cancer?
Most people have cancer in their family history. This is because cancer is so common: about one in three Americans will develop some type of cancer at some point in their lifetime. Cancer is the second leading cause of death for adults in this country.
When several people in the same family have the same type of cancer, it is usually difficult to know why this has occurred. Sometimes it can be coincidental or perhaps better described as bad luck. Some cancers, such as breast and prostate, are so common that it is not especially unusual for someone to have two affected relatives by chance alone. Sometimes, multiple cases of cancer can be related to common lifestyle and/or shared environment. It is also likely that some families have genetic variations that can result in greater sensitivity to environmental factors, causing higher chance of developing cancer.
Rarely, multiple cases of cancer in a family will be related to errors in genes (mutations) that result in a greatly increased risk for certain cancers.
What should I do if I am worried about having an inherited predisposition to cancer?
If you have concerns about your personal and/or family history for cancer, you should talk to your doctor or nurse practitioner who can help you decide if an appointment in Genetics would be useful. If you have multiple cases of breast and/or ovarian cancer, or multiple cases of colon cancer in your family and would prefer to speak directly with someone in Genetics, call your closest Kaiser Permanente Genetics Department.
If you are worried about your family history of cancer, you may want to consider collecting medical records (especially pathology reports) from people in your family who have had cancer. These may be useful to you in the future, and are often important in a genetic evaluation of your family. It may be harder to get records as the years pass, so it is usually better to take this step sooner rather than later.