Hereditary nonpolyposis colon cancer: (Lynch syndrome I and II). A challenge for the clinician.

HNPCC is common and accounts for approximately 4-6% of the total colorectal cancer burden. We have reviewed the clinical and pathology aspects of HNPCC and have made suggestions for surveillance and surgical management which would be responsive to HNPCC's natural history. Because of the proximal predominance of colonic cancer and its early age of onset, we recommend that colonoscopy be initiated by age 25 years. Once the diagnosis of colorectal cancer is established, the treatment of choice is subtotal colectomy. Attention must also be given to extracolonic sites of cancer predilection in Lynch syndrome II. A new histology finding in HNPCC is the flat adenoma. More research will be required in order to determine this lesions's status as a potential marker for HNPCC.