The majority of colorectal cancers are sporadic, meaning that a non-inherited gene mutation develops during a person’s lifetime that causes cancer to develop. These are called acquired genetic mutations.
About 5% of all colorectal cancers develop from an inherited gene mutation passed down from at least one parent. Individuals with hereditary gene mutations related to colon cancer have a higher chance of receiving a diagnosis than the average person. They also tend to occur at an earlier age than non-inherited cases of colorectal cancer.
Some mutations, called inherited mutations, are passed from generation to generation. These inherited 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.
The most common genetic syndromes may include:
Rare inherited syndromes linked to colon and rectal cancers and their associated genes include:
There are also genes that, when mutated, can lead to colorectal cancer. Unlike inherited mutations that affect the entire body, acquired mutations only affect cells that come from the original mutated cell. These mutated cells then begin to multiply, resulting in cancer. Certain risk factors such as smoking, diet, and UV radiation from the sun may play a role in the development of these mutations, but overall, the reason behind what causes most of them is unclear at this time.
There are various tests available to determine if a genetic mutation is the cause of the cancer. Based on that information, a treatment plan can be created.
There are tests that can be performed to determine if an individual has an inherited gene mutation. If some of these indicators are present, testing for inherited mutations may be suggested:
At Compass Oncology, our genetic counseling team will meet with the patient to discuss genetic testing if the oncologist feels that there are indicators of an inherited gene mutation. Genetic counseling can help people consider the risks, benefits, and limitations of genetic testing in their particular situations as well as how to discuss results with their families.
The test for FAP syndrome involves examining DNA in blood cells called lymphocytes (white blood cells), looking for mutations in the APC gene. Genetic testing for HNPCC involves looking for mutations in four of the five genes identified that are associated with HNPCC.
It’s important to understand that these tests may not identify all gene mutations that cause certain genetic syndromes, such as the ones listed above. In some families, additional mutations may be present that cause these syndromes, which the commonly used gene tests cannot detect.
Knowing your family medical history for colorectal cancer could indicate whether you are at an increased risk for acquiring the disease. It’s also a good idea to be aware of family members who have been diagnosed with multiple cancers, especially at a young age. The more you understand your family’s cancer history, the better equipped you’ll be to take a proactive approach to cancer prevention. If you are in a family with a high risk of genetic predisposition, you may consider testing.
Biomarker testing is a relatively new process as part of a colorectal cancer diagnosis. The tumor is tested for various genetic mutations that are not related to an inherited gene mutation. The results of these tests can guide the treatment plan based on what is most likely to work best.
At Compass Oncology, our cancer specialists are here to help you or a loved one through the colorectal cancer diagnosis and genetic testing process. Request an appointment at one of our cancer centers in Portland, Oregon, or Vancouver, Washington, for a consultation.