Genetics Northern California

Colon Cancer

What is the chance for colon cancer?
What causes colon cancer?
Can colon cancer be inherited?
How do you identify someone who might have a gene mutation that predisposes to colon cancer?
How can I learn more about my personal risks for carrying a mutation in a cancer susceptibility gene?
What should I expect if I call my Genetics Department to inquire about my colon cancer risk?
How can I prepare before contacting the Genetics Department?

What is the chance for colon cancer?
Anyone can get colon cancer. It is the third most common cancer diagnosis. The lifetime risk for colon cancer is about 1 in 20, or about 5%.

What causes colon cancer?
Colon cancer is due to mutations in genes that control the growth of cells in the colon. Most mutations happen randomly over a lifetime and are not inherited.

Can colon cancer be inherited?
Cancer is not inherited, but you can inherit a genetic risk for cancer. Cancer susceptibility genes are genes that can make it more likely to develop cancer over a lifetime.  Only about 5-10% of people with colon cancer have an inherited risk for cancer due to a mutation in a cancer susceptibility gene.
For more information:

Hereditary Colon Cancer: Should you have genetic testing?

What to Expect at Your Genetics Appointment

There are two genetic conditions that account for most cases of inherited susceptibility to colon cancer:

Lynch syndrome (also called HNPCC or hereditary non-polyposis colon cancer)
Lynch syndrome is a condition caused by a mutation in one of several different genes. It is the most common cause of inherited colon cancer susceptibility.  Families with Lynch syndrome, often have several family members with colon cancer, usually diagnosed at a young age. Women in these families are more likely to develop uterine or ovarian cancer. There are also other cancers that happen more often in families with Lynch syndrome: stomach, urothelial (kidney/urinary tract), brain, small intestine, pancreatic.
For more information: Lynch syndrome

Familial Adenomatous Polyposis (FAP) 
FAP is caused by a mutation in a gene called APC. This condition accounts for about 1% of colon cancers. Individuals who have classic FAP usually develop hundreds of polyps in the colon and other parts of the GI tract. Without surgery, these polyps eventually lead to cancer. Polyps can start forming in the teens or 20's, so this condition needs close follow-up starting in childhood. A milder form of FAP can also happen, with fewer polyps and a later onset of cancer.
For more information: Familial Adenomatous Polyposis (FAP) syndrome

How do you identify someone who might have a gene mutation that predisposes to colon cancer?
We identify those at a higher genetic risk by reviewing the family history and directly testing the tumor.

Family History:  A review of the family history incudes noting the type(s) of cancer in the family, the age of the person when each cancer was diagnosed, and the relationship between family members with cancer. Inherited risk for colon cancer can come from either parent, so we consider both sides of the family (maternal and paternal).

Here are some findings that increase the chance for an inherited risk for cancer:

  • Cancer that happens earlier than usual

  • Individuals with more than one type of cancer

  • Many relatives with similar cancers 

Use our Family History Form to gather information about cancer in your family.


Tumor Testing: Tests done directly on cells from a tumor can also help find individuals who are more likely to have an inherited risk for cancer.

Colorectal Cancer: Immunohistochemistry (IHC) testing

To learn more about genetic testing: Hereditary Cancer Risk: Who should be tested first?

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How can I learn more about my personal risks for carrying a mutation in a cancer susceptibility gene?
You can learn more about your personal risks by having your family history reviewed by a genetic counselor. You may be referred to your local Genetics Department by your healthcare provider, or you may call your closest Kaiser Permanente Genetics Department yourself.  

What should I expect if I call my Genetics Department to inquire about my colon cancer risk?
Individual counseling or a genetic counseling class may be scheduled to give you general information about the genetics of colon cancer.  We may take a complete family history, including medical information on family members with and without cancer. Medical records or death certificates may be requested to help estimate your risk. Once we have obtained a cancer history from you, you are given a personalized estimate of your inherited risk for colon cancer. DNA testing for cancer susceptibility genes may or may not be offered, depending on your risk and your family history. Genetic information often has an impact on many individuals within a family, and may be emotionally complicated by the nature of relationships within a family. These issues are considered and discussed during the process of genetic counseling.

How can I prepare before contacting the Genetics Department?
Before contacting Genetics, it is helpful if you gather medical information about your family. It is especially useful to know any type of cancers in the family and the person's age when each cancer was diagnosed.  
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Last reviewed:    November 30, 2017
Reviewed by:     Kimberly Barr, MS, LCGC