By Miriam Komaromy, MD

Reviewed By Peggy Conrad, MS, CGC and Jonathan Terdiman, MD
Last Updated August 1, 2000

Hereditary nonpolyposis colorectal cancer (HNPCC, also known as Lynch Syndrome) — a hereditary syndrome triggered by mutations in a handful of genes — puts individuals at increased risk for a number of types of cancer. Not surprisingly (given the syndrome's name), the most common of these is colon cancer. Unless aggressive steps are taken to prevent this from happening, approximately eighty percent of people who have been diagnosed with the syndrome will go on to develop colon cancer. This increased risk, along with differences in the way HNPCC-associated colon cancer presents itself, has led to differences in the way doctors screen for and treat the disease in individuals who have inherited HNPCC syndrome.

Screening for HNPCC

Colonoscopy is the only truly effective method of detecting all of the potential cancerous colon polyps in people with HNPCC.

Colon cancer develops the same way regardless of whether an individual has HNPCC — with the appearance and subsequent growth of polyps (small mushroom-like knobs of flesh) in the colon or rectum. However, in people who have HNPCC, these polyps generally develop at an earlier age, and are more likely to become cancerous. They are usually located in a different part of the colon — all of which lead to a number of differences in the way physicians screen for colon cancer among this population.

• click image for larger representation

  Screening begins at a younger age, and occurs more frequently. The average age of onset for colon cancer in the general population is approximately 65. However in individuals with HNPCC, that diagnosis is likely to be made at a significantly younger age (44 on average). For this reason — and because their polyps are more likely to become cancerous — physicians recommend that for individuals with HNPCC, colon cancer screening should begin earlier (at age 25) and take place more frequently (annually) than for members of the population at large.
• Colonoscopy is the preferred screening method. Most colon cancers develop from polyps in the lower third of the colon. However, in people who have inherited HNPCC, colon cancer typically develops higher up, from polyps located in the proximal colon (on the right side of the abdomen). This means that the normal method of screening for colon cancer — flexible sigmoidoscopy — is not sufficient for those with HNPCC because it only allows doctors to examine the lower third of the colon (approximately). Instead, experts recommend colonoscopy for people with this hereditary syndrome. In both procedures, the physician places a thin, flexible tube with a light and a viewing camera at one end of the patient's rectum and guides it along the colon to check for polyps and other abnormalities. Although similar in concept to the flexible sigmoidoscopy, the colonoscopy allows physicians to examine the entire length of the colon.

Treatment

Researchers have also discovered that — as compared to the general population — HNPCC patients who have been diagnosed with one colon cancer are more likely to develop a second, separate cancer at the same time but in a different part of the colon. In addition, approximately 20 percent of HNPCC patients who have had a colon cancer removed will later go on to develop another cancer of the colon or rectum. This leads to differences in the way physicians treat colon cancer in people who have HNPCC.

If caught early, before it has spread, colon cancer is usually treatable through surgical removal of not only the cancer, but also the section of colon where the cancer occurred. This is the case whether or not a person has HNPCC. However, if a person who has HNPCC goes on to develop another colon cancer, his or her doctor may recommend a total colectomy, a procedure in which the entire colon is removed. This more drastic surgery is usually performed because of the high likelihood that a patient with HNPCC will develop another cancer elsewhere in the colon if the entire colon is not removed.

Prevention

In some cases, even HNPCC patients who have not developed colon cancer may still consider undergoing colectomy as a preventive measure. This procedure is referred to as a prophylactic colectomy.

Although this may sound extreme, doctors sometimes recommend prophylactic colectomy as a preventive measure because HNPCC patients are at such significant risk for developing colon cancer. However, it's important to understand that the procedure is not specifically recommended; in fact, only a minority of patients with the HNPCC risk factor actually choose this option.

References

Ahlquist, D. (1995). Aggressive polyps in hereditary nonpolyposis colorectal cancer: targets for screening. Gastroeneterology. 108(5): 1590-92.

Box, J., M. Rodriguez-Bigas, et al. (1999). Clinical implications of multiple colorectal carcinomas in hereditary nonpolyposis colorectal carcinoma. Dis Colon Rectum. 42(6): 717-721.

Burke, W., G. Petersen , et al. (1997). Recommendations for follow-up care of individuals with an inherited predisposition to cancer: Hereditary nonpolyposis colon cancer. JAMA. 277(915-919).