There are two well-recognized hereditary syndromes in which cancer can develop in young people. The first is Familial Adenomatous Polyposis (FAP). This is a disease in which affected people develop hundreds to thousands of precancerous polyps in the colon. Unless the colon is removed, 100% of these patients will get colorectal cancer, usually by their late 30s. The disease is inherited directly from an affected parent (autosomal dominant inheritance), and the average age for polyp development in this syndrome is the mid-teens.
If a family is known to have FAP, the affected parent and at-risk children may be screened for a gene mutation with a genetic test. Children who do not or cannot have genetic tests should start having sigmoidoscopies or colonoscopies at about 10 or 12 years old and every 6 to 12 months to look for polyps. Once numerous polyps start developing, surgery is planned. The good news about this disease is that the surgical options are very good and now the colon can often be removed by a laparoscopic approach called colectomy. The bowel is put directly back together and no bag is necessary.
The other disorder is Hereditary Non-Polyposis Colorectal Cancer (HNPCC). In this syndrome, cancers also occur early and develop from polyps. The disease also can present at a later age. The standard recommendation is colonoscopy in at-risk children of affected families beginning at age 25 and repeated every two years. Genetic testing may also be helpful.
As you can see, there are specific recommendations for children in families with high rates of colon cancer. However, the specific syndrome must be known. It is very important for children from families with FAP or HNPCC to be seen by experts who have experience with these syndromes and in institutions where genetic counseling and testing services are available.