Colorectal Genetics & Risk Factors
As with all cancers, there are certain things that put you at risk for acquiring the disease— some of which can be controlled, and some that can’t. And, because there’s no concrete way to know if or when colorectal cancer will develop, it’s highly important to learn more about what those risks are so you can take measures to reduce the likelihood of getting the disease.
How Genetics Play a Role in Colorectal Cancer
As mentioned earlier, there are some risk factors you simply have no control over. Your genes are one of them. When it comes to inheriting a genetic mutation that can cause colorectal cancer, the percentage is slim—less than 10%. The majority of colorectal cancer cases are caused by a mutation of a gene that is acquired during a person’s lifetime (non-genetic).
Inherited gene mutations
In general, cancer is caused by certain changes to genes that control the way our cells function, especially how they grow and divide. Some mutations, however, are ones that can be passed from generation to generation.
These mutations, called inherited (hereditary) mutations, are present throughout a person’s life in nearly every cell of the body. Common genetic syndromes, which are disorders caused by one or more abnormalities in the genome, have been linked to colorectal cancer.
Genetic syndromes may include:
- Familial adenomatous polyposis (FAP) and Gardner syndrome. These syndromes are caused by inherited changes in the APC gene, which is a tumor suppressor gene that helps keep cell growth in check. Changes in the APC gene can result in hundreds of polyps to form in the colon.
- Lynch syndrome (hereditary non-polyposis colon cancer, or HPCC). This syndrome is caused by changes in genes that help damaged DNA repair itself. Mutations of genes like MLH1, MSH2, MLH3, MSH6, PMS1, and PMS2 keep DNA errors from being fixed. This can affect growth-regulating genes, thus leading to the possible development of cancer.
- Peutz-Jeghers syndrome. A syndrome caused by inherited changes in the tumor-suppressor gene STK11 (LKB1).
- MUTYH-associated polyposis. This syndrome is caused by mutations in the MUTYH gene, which plays a role in how the cell checks the accuracy of DNA when cells divide.
Acquired gene mutations
In other cases, some gene mutations simply happen during a person’s lifetime. Unlike inherited mutations that affect the entire body, acquired mutations only affect cells that come from the original mutated cell.
Certain risk factors such as smoking, diet, and UV radiation from the sun may play a role in the formation of these mutations, but overall, the reason behind what causes most of them is unclear.
Genetic Testing for Colorectal Cancer
Fortunately, there are ways to determine if you are at an increased risk for colorectal cancer based on your genes. Genetic testing for hereditary cancer syndromes can indicate whether you show signs of any genetic syndromes, such as the ones listed above.
These tests can also show whether family members without obvious disease have inherited the same mutation as a family member who carries a cancer-associated mutation.
Factors that suggest a genetic contribution to colorectal cancer include:
- A strong family history of colorectal cancer and/or polyps
- Multiple cancers in a patient with colorectal cancer
- Being of an early age at diagnosis
Since genetic tests are usually requested by physicians, we recommend that you speak to yours about your family health history. If your physician feels as though you’d be a good candidate for genetic testing, we encourage you to make an appointment to meet with a cancer genetic counselor at Rocky Mountain Cancer Centers (RMCC). Genetic counseling can help you consider the risks, benefits, and limitations of genetic testing in your particular situation.
Other Colorectal Cancer Risk Factors
In addition to genetics, there are other risk factors that are completely out of your control. These can include:
- Age. The risk of colorectal cancer increases as people get older. Colorectal cancer can occur in young adults and teenagers, but the majority of colorectal cancers occur in people older than 50.
- Gender. Men have a slightly higher risk of developing colorectal cancer than women.
- Family history of colorectal cancer. Colorectal cancer may run in the family if your first-degree relatives (parents, brothers, sisters, children) or other family members (grandparents, aunts, uncles, nieces, nephews, grandchildren, cousins) have had colorectal cancer.
- Inflammatory bowel disease (IBD). People with IBD, such as ulcerative colitis or Crohn’s disease, may develop chronic inflammation of the large intestine. This increases the risk of colorectal cancer. Keep in mind that IBD is not the same as irritable bowel syndrome (IBS). IBS does not increase your risk of colorectal cancer.
- Adenomatous polyps (adenomas). It’s important to understand that polyps are not cancer. However, some types of polyps called adenomas can develop into colorectal cancer over time.
- Personal history of certain types of cancer. If you have a personal history of colorectal cancer or have had ovarian cancer or uterine cancer, you are more likely to develop colorectal cancer.
- Race. Black people have the highest rates of sporadic, or non-hereditary, colorectal cancer in the United States.
Sometimes, the lifestyle choices you make can also contribute to your risk for colorectal cancer. Risk factors that you do have some control over include:
- Physical inactivity and obesity. If you live an inactive lifestyle (no regular exercise and a lot of sitting) or are overweight or obese, you may have an increased risk of colorectal cancer.
- Nutrition. Current research consistently links eating more red meat and processed meat to a higher risk of the disease. Other dietary factors have also been looked at to see if they affect the risk of developing colorectal cancer.
- Smoking. Recent studies have shown that smokers are more likely to die from colorectal cancer than nonsmokers. If you smoke, we recommend that you quit.
Remember, different factors cause different types of cancer— and although there is no proven way to completely prevent this disease, you may be able to lower your risk. We at RMCC recommend that you take control of your health by understanding your family history, striving to make good lifestyle choices, and seeing your physician for regular colorectal cancer screenings. If the time comes when you need us, know that we are here to help.