What Are Genetic Colon Cancer Syndromes?
Colon cancer is the third-leading cause of cancer deaths for both men and women in the United States. Colon cancer is often referred to as colorectal cancer because colon cancer is often present in the rectum as well. However, it is possible to have rectal cancer alone, but the comorbidity of rectal and colon cancer together is very high. While the mortality rate of colon cancer has been decreasing due to diagnostic testing such as colonoscopy, if colon cancer is not detected early, the mortality rate is exceptionally high. For example, a patient with stage IV colon cancer has a 12 to 14 percent five-year survival rate. If colon cancer is discovered while it is still localized (stage I), patients have a 91 percent five-year survival rate.
Looking at the statistics reveals that early detection is crucial—and saves lives. Colonoscopy is the gold standard for early detection of colon cancer, but family history is important too. While researchers have not pinpointed the exact cause of why colon cancer develops, there is a definitive hereditary link. Also, certain forms of colon cancer are clearly linked through genetics, such as Lynch syndrome.
Why Is Family History So Important?
Colorectal cancer is one of the deadliest cancers because, in most cases, patients are asymptomatic. When someone begins to feel symptoms of colon cancer, it’s typically a sign that the cancer has progressed to later stages, such as spreading to the lymph nodes or vital organs. In these stages, the mortality rate increases significantly. It’s important to inform your doctor if you have any immediate family history of colon or rectal cancer, polyps, and other gastrointestinal conditions such as inflammatory bowel disease (IBD). The American Cancer Society recommends that both men and women have their first colon cancer screening at age 45. However, if you have risk factors such as an immediate family history of colon cancer, you have a greater risk of developing the cancer earlier. Those with a family history of colon cancer can opt for genetic testing, to be screened for colorectal cancer earlier than 45, or both.
How Are Genes Connected to Colon Cancer?
Your healthcare provider may recommend genetic testing. If you have a noted family history of colonic cancers or GI conditions. There are specific types of colon cancer that are hereditary, including Lynch syndrome (hereditary non-polyposis colon cancer), familial adenomatous polyposis (FAP) or attenuated FAP (AFAP), Gardner syndrome, Peutz-Jeghers syndrome, and MUTYH-associated polyposis (MAP).
- Lynch syndrome occurs when genes fail to help a cell repair damaged DNA. It is caused by a mutation in the MLH1, MSH2, MSH6, PMS2, and EPCAM genes.
- FAP, AFAP, and Gardner syndrome all affect the APC gene. Typically, this gene prevents tumors from forming, but if a patient inherits an altered APC gene, it fails to do its job, and polyps can form.
- Peutz-Jeghers syndrome is similar to FAP and AFAP as it concerns the STK11 (LKB1) gene and is a tumor suppressor. If a mutated gene is inherited, polyps form.
- MAP is caused by a MUTYH gene mutation. When this gene mutates, it fails to fix problems during cell division.
Many cases of colon cancer stem from these acquired gene mutations. However, patients will be asymptomatic and may not know they have mutated genes present.
What Is Genetic Testing for Colon Cancer?
If you meet certain criteria and risk factors for colon cancer, you can opt for genetic testing prior to a colon cancer screening. Predictive genetic testing looks for acquired mutated genes, putting a person at a higher risk of developing colon cancer. Genetic testing itself is a simple process. First, you will meet with a genetic counselor to discuss the test and advise you on what to expect. Then, you will submit either a saliva swab or have a blood test to determine if you have any of the known hereditary colon cancer gene mutations.
What Are the Screening Tests for Genetic Colon Cancer?
Some patients opt for genetic testing, some opt for early screenings, and some opt for both. Your gastroenterologist may order different diagnostics based on your individual case. Some of the diagnostic tests may include:
- Colonoscopy (a long, thin tube that examines the colon via insertion into the anus and rectum) is first-line when it comes to screening for colon cancer, particularly for people who have genetic mutations that can increase one’s chance of getting colon cancer.
- Digital rectal exam. This simple exam involves your physician inserting a lubricated and gloved hand into your rectum to feel if there are any abnormalities.
- Flexible sigmoidoscopy. A sigmoidoscopy is similar to a colonoscopy, especially when it comes to prep; however, this test doesn’t have the ability to examine the entire colon. This test looks for problems in the rectal area and lower large intestine.
- Stool testing You’ll provide a stool sample for your provider, and it will be sent to the lab to be analyzed for blood or abnormal DNA in the stool.
- Barium enema (lower GI series). During this test, barium (also known as contrast) is inserted into the rectum via a tube. Afterward, an X-ray is taken, and the contrast material shows abnormalities in the colon, such as polyps.
If genetic mutations or colon cancer are discovered, your gastroenterologist will then discuss the next steps or treatment options.