By: Miriam Komaromy, MD

Reviewed by Peggy Conrad, MS, CGC and Jonathan Terdiman, MD

If members of your immediate family have been diagnosed with colon cancer, your risk of developing the disease is greater than the risk for the general population. In fact, studies show that twenty percent to twenty-five percent of colon cancer patients have a family history of the disease. However, assessing your personal risk is a complicated undertaking, and to do so accurately, you and your doctor will need to analyze the medical history of your entire family.

Familial History or Hereditary Syndrome?

• Multiple family members diagnosed with colon cancer
• A very young age of diagnosis of colon cancer in some family members
• Diagnoses of other, associated cancers in some family members

Signs of Familial Colon Cancer

In contrast, if just one member of your immediate family was diagnosed with colon cancer at a relatively young age, and the pattern of disease in your family is not sufficient to indicate FAP or HNPCC, you may have what experts refer to as a familial (as opposed to a hereditary) colon cancer history. If this is the case, you are still at higher risk for colon cancer than are members of the general population — just not as high a risk as someone who comes from a family that has been diagnosed with one of the hereditary colon cancer syndromes. For screening purposes, someone is said to have a significant familial history of colon cancer if he or she fits the criteria in the following chart:

Genetics and Familial Colon Cancer

Family History and Risk

If you have a familial history of colon cancer, your own risk for the disease will depend on how many members of your family have been diagnosed with colon cancer, and at what age. The relationship is simple: The more family members affected and the earlier the age of diagnosis, the greater your own risk. Here are some basic examples:

• If you have a sibling or parent who has been diagnosed with colon cancer, your own risk of developing colon cancer is about 1.7 times as great as if you had no family history of colon cancer.
• If you have two immediate family members with colon cancer, your risk is 2.7 times as great as if you had no family members with colon cancer.
• The risk is further increased if family members were diagnosed with colon cancer at an early age

Polyps and Risk

Another factor indicating an increased risk of colon cancer is a family history of colon polyps. However, there are several types, and only those classified as adenomatous polyps appear to increase the risk of colon cancer. (To determine a polyp's type, a pathologist generally needs to examine the polyp tissue after it has been removed.) A family history of adenomatous colon polyps appears to increase your risk of colon cancer to about the same extent as does a family history of colon cancer.

First-degree relatives of someone with an adenomatous colon polyp have 1.7 times as great a risk of developing colon cancer as people who have no family history of these polyps. The age at which the polyp is diagnosed is also important. If a family member's polyp is diagnosed before the age of 60, the risk of another family member developing colon cancer is 2.6 times greater than if the polyp is diagnosed after the age of 60. If a family member's polyp is diagnosed before that person reaches age 50, other family members are at four times greater risk for developing colon cancer than if that polyp was diagnosed when the individual was older than 60.

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Screening and Prevention

Even though scientists and doctors do not yet fully understand the genetic basis for familial colon cancer, they have uncovered enough information to believe that people with a familial history should be screened earlier, more often, and more extensively than people who do not have a family history of the disease. Some of these reasons include:

Colon cancer appears to develop somewhat earlier in patients with a familial history of the disease than it does in members of the general population.

Polyps may occur more frequently, with a greater risk of becoming cancerous in people with a familial history of colon cancer.

Colon cancer is somewhat more likely to occur higher up in the colon in people with a family history of the disease than people with no family history.

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More on Screening and Prevention for Familial Colon Cancer

References

Ahsan, H. et al. (1998). Family history of colorectal adenomatous polyps and increased risk for colorectal cancer. Annals of Internal Medicine, 128(11):900-905.

Burt, R. (1997). Screening of patients with a positive family history of colorectal cancer. Gastrointestinal Endoscopy Clinics of North America, 7(1):65-79.

Fuchs, C. et al. (1994).A prospective study of family history and the risk of colorectal cancer. N Engl J Med, 331(25): 1669-74.

Winawer, S. et al. (1996). Risk of colorectal cancer in families of patients with adenomatous polyps: National Polyp Study Workgroup. N Engl J Med, 334:82-87.