Hereditary Non-polyposis Colorectal Cancer (HNPCC) is the most common known hereditary cause of colon cancer. It accounts for between 2-5% percent of all colon cancer cases. Since people with HNPCC may have no symptoms or polyps, the key to identifying this syndrome and the risk for developing colorectal cancer lies in one's family history.
 
The following are the criteria to make a clinical diagnosis of HNPCC (however not all persons or families with HNPCC will meet these criteria):

• At least three members of your family diagnosed with a cancer associated with HNPCC (colon, endometrium (uterine), small bowel, ureter, or renal pelvis.) Not all relatives need to have the same kind of cancers.
• One of these three family members must be a first-degree relative (parent, offspring, or sibling) of the other two. 
• Relatives with cancer involve at least two successive generations. 
• At least one of these relatives must have been diagnosed with cancer before age 50. 

Although polyps need not occur in HNPCC for a person to develop cancer, people with HNPCC can have polyps and in fact are more likely to develop polyps, and at a younger age, than people without HNPCC. Patients with HNPCC develop colorectal cancer at an accelerated rate and thus need frequent screening.
 
Members of families with HNPCC should strongly consider some special colon cancer screening and prevention options including:

• A colonoscopy every one to two years after you reach the age of 20 to detect any abnormalities, or polyps, on the inside walls of your colon.
• Women should also be screened for endometrial cancer (also called cancer of the uterus)
• Screening for other cancers may be recommended depending on family history