Hereditary Colorectal Cancer

Abstract

he annual incidence of colorectal cancer in the unitedStates is approximately 148,300 (affecting 72,600 males and 75,700 females), with 56,600 deaths (in 27,800 males and 28,800 females).1 The lifetime risk of colorectal cancer in the general population is about 5 to 6 percent. 1 Patients with a familial risk -those who have two or more first-or second-degree relatives (or both) with colorectal cancer -make up approximately 20 percent of all patients with colorectal cancer, whereas approximately 5 to 10 percent of the total annual burden of colorectal cancer is mendelian in nature -that is, it is inherited in an autosomal dominant manner.In this review we will focus on the two major forms of hereditary colorectal cancer, familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer.The most important step leading to the diagnosis of a hereditary cancer syndrome is the compilation of a thorough family history of cancer.2-4 A patient and his or her key relatives, working either alone or with a trained nurse or genetic counselor, can compile such a detailed family history.The focus should be on identifying cancer of all types and sites; the family member's age at the onset of cancer; any pattern of multiple primary cancers; any association with phenotypic features that may be related to cancer, such as colonic adenomas; and documentation of pathological findings whenever possible.This information will frequently identify a hereditary colorectal cancer syndrome in the family, should it exist.Molecular genetic testing may then provide verification of the diagnosis, when a germ-line mutation is present in the family.5,6 The primary care physician may wish to refer the patient to a hereditary-cancer specialist and genetic counselor for further evaluation should there be any remaining question about the disorder's clinical or molecular genetic diagnosis and the need for targeted surveillance and management.Once a diagnosis of a hereditary colorectal cancer syndrome is established, the proband's high-risk relatives should be notified, and genetic counseling and DNA testing should be performed in consenting relatives, when such testing is appropriate.In an attempt to reduce morbidity and mortality, surveillance measures may then be instituted that reflect the natural history of the disorder.7 Once it is clear that a patient has a familial form of colorectal cancer, genetic counseling is mandatory and must provide the patient and his or her extended family with important details about their genetic risk of cancer at specific sites, on the basis of the natural history of the hereditary cancer syndrome; the options for surveillance and management; and the availability of genetic testing.8,9 Counseling should be face to face, but a session may include multiple family members.8 The concept of informed consent implies that a patient has received counseling, information, and putative test results and t overall clinical approach