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HNPCC
  What Is HNPCC?

By Miriam Komaromy, MD

Reviewed by Peggy Conrad, CGC and Jonathan Terdiman, MD




Hereditary nonpolyposis colorectal cancer
(HNPCC) is the most common known hereditary cause of colon cancer. In fact, HNPCC accounts for between two and five percent of all colon cancer cases.

 
 
 

What Is HNPCC?

HNPCC is a hereditary syndrome that is caused when a person inherits a mutation in one of five different genes. If people born with HNPCC do not undergo early and regular screening, they have a much higher risk of developing colon cancer than the general population if they do not undergo early and regular screening.

 

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About two to five percent of all colon cancer cases are attributed to HNPCC, also called Lynch Syndrome, after Dr. Henry Lynch who realized that it was a separate disorder from other hereditary colon cancer syndromes.

Certain things are misleading about the name of the syndrome hereditary nonpolyposis colon cancer. First, HNPCC is not a form of cancer, it is only a syndrome that puts people at high risk for colon cancer. Second, even though the name has nonpolyposis in it, people with HNPCC will still develop colon polyps as a precursor to colon cancer. Scientists simply use this term to distinguish HNPCC, which causes a small number of polyps to develop, from another hereditary colon cancer — familial adenomatous polyposis syndrome — in which thousands of polyps develop.

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When HNPCC Leads to Colon Cancer

Although a person can have HNPCC without actually having colon cancer, mutations in the genes that cause HNPCC dramatically increase the risk of developing colon cancer.

Nearly all colon cancers begin as noncancerous polyps — or mushroom-like growths inside the colon. People with HNPCC are much more likely to develop these polpys, and tend to develop them at a younger age than people without HNPCC.

 

 
People with HNPCC
The General Population
Percent who will develop colon cancer
80*
4
Average age that colon cancer develops
44
65
*Without early and regular screening

 

HNPCC also puts patients at higher risk of some other forms of cancer.

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Family Medical History

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People with HNPCC need to be screened earlier because of their tendency to develop colon cancer at a young age.

Colon cancer typically does not produce symptoms until it is too late to successfully treat the disease. However, there are effective early detection methods. In the general population, such screening for cancer is not necessary before age 50. But, people with HNPCC need to be screened earlier because of their tendency to develop colon cancer at a young age. But how do doctors know who has HNPCC if there are no symptoms? The key lies in one's family history.

If either of your parents has HNPCC, you have a 50 percent chance of inheriting the altered gene and thus the syndrome — a pattern of inheritance called autosomal dominant inheritance. Using this knowledge about how HNPCC is passed down through families, health professionals with experience in genetics can look for clues.

Because family histories can be complicated, a group of doctors and researchers developed guidelines called the "Amsterdam II Criteria" to help identify patients who might have HNPCC.

 

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The Amsterdam II Criteria
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hnpccAt least three members of your family must have been diagnosed with a cancer associated with HNPCC - cancer of the colon, endometrium, small bowel, ureter, or renal pelvis.
(Note: Not all relatives must have the same kind of cancers.)


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One of the three family members must be a first-degree relative (parent, offspring, or sibling) of the other two.

At least two successive generations of your family should be affected.

hnpccAt least one of these relatives must have been diagnosed with cancer before age 50.

hnpccYour doctor must have ruled out familial adenomatous polyposis (or FAP, the other hereditary colon cancer syndrome) as the cause of colon cancer in your family.

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Limitations of Screening Criteria

It is important to note that many, but not all, families with HNPCC meet these criteria. In other words, your family could still have HNPCC even if you don't meet all the Amsterdam II criteria. These guidelines become particularly unreliable if you come from a small family.

If you believe your family history of cancer is suggestive of HNPCC, you should discuss it with a genetic counselor or geneticist who is familiar with this particular disorder. Although many families do not fit the profile of the Amsterdam II criteria, many might still benefit from genetic testing, and should follow screening and prevention guidelines designed for patients with HNPCC.

 

Amsterdam II Criteria for HNPCC
KEY: HNPCC-associated cancers = colon, endometrium, small bowel, kidney (renal pelvis), and ureters
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Screening and Prevention

The main way that doctors and genetic counselors figure out if you have HNPCC is by looking at the types of cancer and age at which cancer developed in you or your family. If it looks like your family does have HNPCC, the next step usually involves looking at tumors from people in your family (if they are available). If the tumors suggest that there is a detectable genetic error predisposing your family to HNPCC, the next step is a genetic test to try to identify the error. If someone in your family is found to have an error in one of the genes associated with HNPCC, then other family members can be tested for the same error to find out if they too have inherited the predisposition to HNPCC.

 

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Members of families with HNPCC should strongly consider some special colon cancer screening and prevention options. These include having your doctor perform 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. After the age of 40, you should undergo this procedure annually. Women should also be screened for endometrial cancer (also called cancer of the uterus).

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References

Lynch, H. (1996). Hereditary nonpolyposis colorectal cancer (Lynch Syndrome): An updated review. Cancer 78: 1149-1167.

Rodriguez-Bigas, M. et al. (1997). A National Cancer Institute workshop on hereditary nonpolyposis colorectal cancer syndrome: Meeting highlights and Bethesda guidelines. Journal of the National Cancer Institute 89(23): 1758-1762.

Syngal, S. (2000). Hereditary nonpolyposis colorectal cancer: A call for attention. J Clin Oncology 18(11): 2189-91.

Vasen, H. et al. (1999). New clinical criteria for hereditary non-polyposis colorectal cancer (HNPCC, Lynch Syndrome) proposed by the International Collaborative Group on HNPCC. Gastroenterology 116: 1453-1456.

 

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