About Cancer and Genetics Cancer that runs in families is called hereditary or familial cancer. In a family with hereditary cancer, multiple family members have the same or related cancers, and the cancers strike at an earlier than average age. Genetics: Breast and Ovarian Cancer Only 5 to 10 percent of breast and ovarian cancers can be traced to genetic factors. This means the majority of breast and ovarian cancers are not inherited. Genetics: Colorectal Cancer Certain types of colorectal cancer occur within families. These rare cancers include familial adenomatous polyposis, hereditary nonpolyposis colon cancer, and Turcot syndrome. Genetics: Other Cancers Melanoma skin cancer has a genetic component in 5 to 10 percent of cases. (The majority is caused by exposure to ultraviolet radiation.) Other cancers that are tied to genes are prostate, lung, and thyroid cancer. Genetic Testing Genetic testing takes several forms. Diagnostic testing is used to identify or confirm the diagnosis of a disease in a person or a family. Predictive genetic testing determines the chances that a healthy person might develop a certain disease. Carrier testing determines whether a person carries one copy of an altered gene for a particular disease.