Understanding the Genetics of Colorectal Cancer

Heredity factors can increase the risk of some types of cancer, including colorectal cancer. Although the majority of colorectal cancer cases are not caused by genetic mutation it’s important to understand if you or your family might benefit from genetic testing.

Inherited Gene Mutations Related to Colorectal Cancer

Cancer is caused by changes (or mutations) in the DNA inside our cells. DNA is a chemical substance that carries genes. Genes control the different functions of the cell.

When the genes become abnormal, cells can begin to grow out of control. Cancerous tumors are the result of abnormal cell growth and division.

Oncogenes and Tumor Suppressor Genes

Oncogenes are the genes responsible for the growth and division of body cells. Tumor suppressor genes manage cell division and cause cells to die at the right time.

Specific mutations in the DNA can activate the oncogenes and turn off the tumor suppressor genes. This leads to the uncontrolled growth of cells and the formation of malignant tumors.

Hereditary Genetic Syndromes Related to Colorectal Cancer

Research has shown that there are a few genes that can be tested to see if a patient has a hereditary genetic mutation known to make someone more likely to develop colorectal cancer. This gives them the option of talking to their family members about it.  In some cases it can also change how the patient is treated and monitored during follow up care after treatment is complete.

Some genetic syndromes have been linked to colorectal cancer. They include:

Familial Adenomatous Polyposis (FAP)

FAP is a condition caused by mutations in the APC gene. The APC gene is the tumor suppressor gene that regulates the growth of a cell.

An impaired APC gene results in hundreds or thousands of benign polyps in the colon and rectum. There is a 100% chance that one or two of these polyps can turn malignant by the time the person turns 40. There are three sub-types of FAP – attenuated FAP, Gardner Syndrome, and Turcot Syndrome.

Hereditary Non-Polyposis Colon Cancer (Lynch Syndrome)

Hereditary non-polyposis colon cancer or HNPCC accounts for 2% to 4% of all colorectal cancer cases diagnosed every year. An inherited mutation in DNA repair genes like MLH1, MSH2, MLH3, MSH6, PMS1, and PMS2 causes the condition.

People with Lynch syndrome tend to have a few polyps. The polyps can turn malignant when the person is relatively young. Not everyone with Lynch syndrome develops cancer, but the risk is relatively high (about 80%).  

Peutz-Jeghers Syndrome

Peutz-Jeghers Syndrome is characterized by freckles around the mouth, hands, and feet. A particular type of polyp called hamartomas develops in the digestive tract.

Inherited mutations in the tumor suppressor STK11 (LKB1) gene cause the condition. Damages to the gene cause uncontrolled growth of cells that develop into cancer tumors later.

MUTYH-associated Polyposis (MAP)

MAP is caused by changes or mutations in the MUTYH gene. The gene oversees how each cell checks the accuracy of DNA during cell division.

People with MAP develop polyps in the colon. Patients must monitor the polyps regularly with frequent colonoscopies. The risk of colorectal cancer and other forms of gastrointestinal tract cancers is high among people with the syndrome.

Acquired Gene Mutations that Can Cause Colorectal Cancer

DNA mutations that occur through the course of your life are called acquired gene mutations. Unlike inherited gene mutations, these DNA changes are not passed on to the next generations.  

Acquired mutations affect only the cells that come from the original mutated cell.

Risk factors that can cause acquired gene mutations are:

  • Obesity and being overweight.
  • An unhealthy diet.
  • Lack of exercise.
  • Excessive alcohol consumption.
  • Smoking.

People with a personal history of inflammatory bowel syndrome, Crohn’s disease, Type-2 diabetes have an increased risk of colorectal cancer. The risk of colorectal cancer is higher in older patients.

Who Is at a Higher Risk for Colorectal Cancer?

Most cases of colorectal cancer are diagnosed in people without a family history of the disease. But, up to one in three people diagnosed with colorectal cancer have at least one family member who has had it earlier.

In families predisposed to colorectal cancer, the risk is more significant when a first-degree relative (a parent, child, or sibling) has had it. In such cases, screening is recommended before the age of 40 and more often than someone of average risk. 

Specific racial and ethnic backgrounds can also increase the risk of colorectal cancer. For instance, African Americans have the highest colorectal cancer incidence rate. Ashkenazi Jews are the ethnic group with the highest risk of colorectal cancer.

People who have been diagnosed with other forms of cancer in the past run a greater risk of colorectal cancer. For instance, men who have been treated for prostate cancer with radiation therapy many years ago may have a risk of rectal cancer.

Genetic Testing for Colorectal Cancer

Not everyone needs to be tested for a genetic mutation related to colorectal cancer. Genetic counseling and testing are recommended for people who meet one or more of the following conditions.

  •   People with a family or personal history of an early cancer diagnosis.
  •  For people with colon polyps - it may be due to an inherited gene mutation.
  •   People with family members with multiple primary cancers.
  •  Family members who have a known genetic mutation.
  •  Families with several cancers linked to a single gene mutation.
  • People with several relatives on one side of the family diagnosed with the same type of cancer.

Telegenetics for Improved Cancer Prevention

Telegenetics works like any other telehealth appointment. At Willamette Valley Cancer Institute and Research Centre, our genetic counselors will be able to help you with all queries regarding colorectal cancer through a virtual meeting.

Based on the answers to our questions about medical family history and other existing health conditions, we will be able to know if you are a candidate for genetic testing. 

Learn more about staging for colorectal cancer.

Request an Appointment with a Cancer Doctor