A syndrome is a group of symptoms or signs that occur together to characterize a disease process, some of which are from abnormal genes or DNA that may increase an individual's risk of developing colorectal cancer. These "hereditary colorectal cancer syndromes" account for up to 10% of all colorectal cancers that are diagnosed. Because not all of these syndromes have not been linked to an identifiable abnormal gene or gene mutation, they are often diagnosed by the symptoms and signs that they cause, which can be most easily divided or categorized into those with multiple colorectal polyps (i.e., "polyposis" syndromes) and those without multiple polyps ("nonpolyposis" syndromes).
There are a number of rare syndromes presenting with multiple polyps or abnormal growths in the colon and rectum, and all of these syndromes are associated with an increased risk of colorectal cancer. The most common of these rare syndromes is "familial adenomatous polyposis" or "FAP". FAP is characterized by having 100 or more polyps called "adenomas" in the colon and rectum, which lead to an increased risk of developing colon and/or rectal cancer. This increased risk has been estimated as high as 100% over a person's lifetime. Without surgical treatment, the average FAP patient starts developing polyps by age 16 and will have colorectal cancer diagnosed by age 40. The abnormal gene most often leading to this condition has a 50% chance of being passed on to a child (this is known as "autosomal dominant"), but 20-30% of cases of FAP-related colorectal cancer will be the first ones in their family to have the abnormal gene that leads to the condition.
The primary treatment for FAP is surgery. Other, more rare, polyposis conditions (not all of which have yet been associated with abnormal genes) including attenuated FAP, serrated polyposis syndrome, and hamartomatous polyposis syndromes have different polyp types and numbers, different associated colorectal cancer risks, and need for different screening tests. Nonpolyposis colorectal cancer syndrome "Hereditary nonpolyposis colorectal cancer" or "HNPCC" is the most common hereditary colorectal cancer syndrome, accounting for 3-6% of all colorectal cancers diagnosed in the United States. It is also associated with high risks of colorectal cancer as well as other cancers (e.g. uterine cancer). Also known as "Lynch syndrome", this describes patients with a known gene mutation of major DNA repair genes and/or who fit particular clinical criteria based on a high risk family history of multiple generations with multiple cancers.
HNPCC patients have a lifetime risk of developing colorectal cancer between 30-72%, with high rates of multiple colorectal cancers appearing at the same time or developing new cancers in the future. There are different cancer rates and different types of cancers that occur depending on which of the abnormal Lynch syndrome genes are present. The condition is inherited in such a way that there is a 50% chance of passing the abnormal gene on to a child, much like FAP.
When a patient has a personal or family history suggestive of a high risk of having hereditary cancer syndrome, there are guidelines to determine whether doing testing for an abnormal gene is appropriate. Genetic counseling can help patients understand their risks and need for gene testing. The companies and institutions that provide gene testing can be found at www.genetests.org, which also provides reviews of the genes and syndromes themselves, as well as how the testing is performed.