Colorectal cancer: genetics and screening.

Colorectal cancer is a common disease in the Western world. Most, if not all, colorectal cancers develop from previously benign adenomas. There are a number of genetic abnormalities including mutations in oncogenes and tumor suppressor genes which either present as a germline, or acquired defects lead to the development of colorectal cancer. Two well-defined hereditary colorectal cancer syndromes exist, hereditary nonpolyposis colorectal cancer syndrome and familial adenomatous polyposis coli, for which genetic testing is possible and advised. Guidelines for screening for colorectal cancer in average, moderate, and high risk patients are available from the American Cancer Society and were updated in 1997. The American Society of Clinical Oncology has published guidelines for genetic testing in a variety of cancers including colorectal cancer.