Genetic mutations play a role in the development of all cancers. Most of these mutations occur during a person’s lifetime, but some mutations, including those that are associated with hereditary cancer syndromes, can be inherited from a person’s parents.
Inherited mutations play a major role in the development of about 5 to 10 percent of all cancers.
The genetic mutations associated with more than 50 hereditary cancer syndromes have been identified, and genetic tests can help tell whether a person from a family with such a syndrome has one of these mutations.
A genetic counselor, doctor, or other health care professional trained in genetics can help an individual or family understand genetic test results.
What is genetic testing?
Genetic testing looks for specific inherited changes (mutations) in a person’s chromosomes,genes, or proteins. Genetic mutations can have harmful, beneficial, neutral (no effect), or uncertain effects on health. Mutations that are harmful may increase a person’s chance, or risk, of developing a disease such as cancer. Overall, inherited mutations are thought to play a role in about 5 to 10 percent of all cancers.
Cancer can sometimes appear to “run in families” even if it is not caused by an inherited mutation. For example, a shared environment or lifestyle, such as tobacco use, can cause similar cancers to develop among family members. However, certain patterns—such as the types of cancer that develop, other non-cancer conditions that are seen, and the ages at which cancer typically develops—may suggest the presence of a hereditary cancer syndrome.
The genetic mutations that cause many of the known hereditary cancer syndromes have been identified, and genetic testing can confirm whether a condition is, indeed, the result of an inherited syndrome. Genetic testing is also done to determine whether family members without obvious illness have inherited the same mutation as a family member who is known to carry a cancer-associated mutation.
Inherited genetic mutations can increase a person’s risk of developing cancer through a variety of mechanisms, depending on the function of the gene. Mutations in genes that control cell growth and the repair of damaged DNA are particularly likely to be associated with increased cancer risk.
Genetic testing of tumor samples can also be performed, but this Fact Sheet does not cover such testing.
Does someone who inherits a cancer-predisposing mutation always get cancer?
No. Even if a cancer-predisposing mutation is present in a family, it does not necessarily mean that everyone who inherits the mutation will develop cancer. Several factors influence the outcome in a given person with the mutation.
One factor is the pattern of inheritance of the cancer syndrome. To understand how hereditarycancer syndromes may be inherited, it is helpful to keep in mind that every person has two copies of most genes, with one copy inherited from each parent. Most mutations involved in hereditary cancer syndromes are inherited in one of two main patterns: autosomal dominant and autosomal recessive.
With autosomal dominant inheritance, a single altered copy of the gene is enough to increase a person’s chances of developing cancer. In this case, the parent from whom the mutation was inherited may also show the effects of the gene mutation. The parent may also be referred to as a carrier.
With autosomal recessive inheritance, a person has an increased risk of cancer only if he or she inherits a mutant (altered) copy of the gene from each parent. The parents, who each carry one copy of the altered gene along with a normal (unaltered) copy, do not usually have an increased risk of cancer themselves. However, because they can pass the altered gene to their children, they are called carriers.
A third form of inheritance of cancer-predisposing mutations is X-linked recessive inheritance. Males have a single X chromosome, which they inherit from their mothers, and females have two X chromosomes (one from each parent). A female with a recessive cancer-predisposing mutation on one of her X chromosomes and a normal copy of the gene on her other X chromosome is a carrier but will not have an increased risk of cancer. Her sons, however, will have only the altered copy of the gene and will therefore have an increased risk of cancer.
Even when people have one copy of a dominant cancer-predisposing mutation, two copies of a recessive mutation, or, for males, one copy of an X-linked recessive mutation, they may not develop cancer. Some mutations are “incompletely penetrant,” which means that only some people will show the effects of these mutations. Mutations can also “vary in their expressivity,” which means that the severity of the symptoms may vary from person to person.