Colon Cancer

What is colon cancer?

Colon cancer, or colorectal cancer, occurs when abnormal cells in the large intestine (colon or rectum) grow uncontrollably, forming tumors. It often begins as polyps, which may turn cancerous over time. While the exact cause is unknown, genetics, diet, lifestyle, and age play key roles.

Some people have inherited genetic syndromes that increase their risk for colon cancer. Genetic testing looks for these inherited syndromes along with changes in DNA that are associated with a greater likelihood of developing cancer.

What is Genetic Testing for Colon Cancer?

Genetic testing looks for changes in your DNA that are known to be associated with an increased risk of cancer. Generally, there are two ways that genetic testing may be used:

• Before a person develops cancer to determine their level of risk
• Following a cancer diagnosis to see if genetic changes may have contributed to the cancer

Genetic tests can help show if members of certain families have inherited a high risk of colon cancer due to inherited cancer syndromes including:

• Lynch Syndrome: Lynch syndrome (formerly known as hereditary nonpolyposis colorectal cancer) is associated with an increased risk of colon and rectal cancer, as well as endometrial, ovarian, gastric, urinary tract, brain, and pancreatic cancers. Lynch syndrome is the most common form of hereditary colon cancer. It is responsible for about 3 percent of all colon and rectal cancer.
• Familial Adenomatous Polyposis Familial adenomatous polyposis (FAP) consists of many precancerous polyps — possibly hundreds or thousands — in the colon and rectum.
• MUTYH-Associated Polyposis (MAP): MUTYH-associated polyposis is marked by multiple precancerous polyps in the colon and rectum, similar in number to that seen in the milder form of FAP.

What does a positive genetic test mean?

Patients identified with a a predisposition for hereditary colorectal cancer can benefit from increased surveillance and preventative steps to better manage their risk for cancer. Information obtained from candidate gene testing may potentially be helpful in guiding clinical management in the future. Also, if an inherited susceptibility is found, family members can be tested to help define their risk. If a pathogenic variant is identified, close relatives (children, siblings, parents) could have as high as a 50% chance to also be at increased risk. In some cases, screening should begin in childhood.