Since cancer is a very common disease, it can be expected that many families will have a history of multiple members having had cancer. This may reflect multiple sporadic cancers within a family, familial cancer or hereditary cancer. Sporadic cancers may be due in large part to environmental exposures such as the sun's ultraviolet rays in skin cancer or smoking in lung cancer. Familial cancers are likely due to a combination of environmental exposures and/or genetic factors. Hereditary cancer is the result of a mutation in a single gene or a single pair of genes.
There are many different types of hereditary cancer. Some forms of hereditary cancer affect primarily one site such as the colon, while others may cause cancer to occur in any of several different sites such as the breast and ovary.
Most hereditary cancers are associated with an age of onset that is 15 to 20 years earlier than their sporadic counterparts. This difference in age of onset represents the average. Among single cases, there can be significant variation; for example, sporadic and familial cancers can occur at an early age, and hereditary cancer may not occur until a later age.
