Hereditary Versus Acquired Genetic Errors
Most cancers form due to genetic damage that occur in specific organs, usually from damage that builds up over a lifetime. These are called sporadic cancers. An example is the genetic damage to lung tissue that builds up over years of cigarette smoking that eventually leads to lung cancer. Usually there is no real family history of these types of cancer.
Clustering of specific types of cancers in families has been known for a long time. You might say you know you are at risk of breast cancer because your two sisters, mother, maternal aunt and first cousin all had breast cancer. It is important to distinguish between people who have a risk of cancer due to one of the hereditary cancer syndromes from people who only have a much lower risk because the cancers in the family do not fit these hereditary syndromes but occur due to sporadic cancer which developed in several family members.
It can sometimes be very difficult to determine if the cancers seen in the family fit a cancer syndrome or fit a series of family members who developed sporadic cancers (bad luck, so to speak), and a cancer genetic counselor can help work through as much family information in order to determine the best cancer risk. The analysis done by a cancer genetic counselor can help determine if a hereditary gene mutation is likely and if a specific cancer genetic test is recommended.