Approximately 25 percent of people with colorectal cancer have at least one relative with colorectal cancer, while 75 percent of cases are in people without a family history of the disease. Approximately 5 percent of colorectal cancers are because of known predisposing genetic factors. This means that the majority of colorectal cancers are, in fact, not inherited. Specifically, 3 to 4 percent of all cases of colorectal cancer are from hereditary nonpolyposis colon cancer, or HNPCC, and about 1 percent are from familial adenomatous polyposis, or FAP.
The following sections will provide an overview to the genetics of colorectal cancer, as well as examples of genetic syndromes associated with an increased risk for colorectal cancer.
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