What Causes Colon Cancer? Understanding Genetics and Risk Factors

In 2022, an estimated 600,000 people will be diagnosed with colon cancer - a highly preventable disease.

You should know your risks for colon cancer and understand that early detection through prevention and screening is proven to dramatically reduce fatalities from colorectal cancer.

When someone considers their risks for colon cancer - the big question often is: “Is it hereditary?”

Surprisingly, most colorectal cancers are found in people without a family history of colon cancer.

When is Colon Cancer Hereditary?

Still, according to the American Society of Clinical Oncology, colon cancer may run in the family if first-degree relatives (parents, brothers, sisters, children) or many other family members (grandparents, aunts, uncles, nieces, nephews, grandchildren, cousins) have had colorectal cancer. This is especially true when family members are diagnosed with colorectal cancer before age 60. If a person has a family history of colorectal cancer, their risk of developing the disease is nearly double. The risk further increases if other close relatives have also developed colorectal cancer or if a first-degree relative was diagnosed at a younger age.

You Have a Family History – Now What?

If you do have a family history of colorectal cancer, your doctor will look at your family history and make decisions about safeguarding your health by recommending that you start screening at a younger age and get screened more frequently, only use colonoscopy as a screening test in place of other tests, and to consider genetic counseling for inherited risk. Genetic counselors are trained to estimate risks based on your medical and family history, determine if genetic testing might help with your medical care, and explain the risks and benefits of genetic testing. It is important to know, however, that some people with a predisposing genetic variation will never get colon cancer, while others will.

Genetic counselors are an important part of Baystate’s Family Cancer Risk Program.

Talk to Your Doctor About Your Family History

Mary-Alice Abbott, MD, PhD, medical geneticist at Baystate Health, recommends knowing your family history and discussing it with your doctor.

“When multiple family members have had cancers, particularly at younger ages, it is important to consider the possibility of a hereditary cancer predisposition syndrome in your family. Genetic testing may show that you are at higher risk for certain cancers, and additional screening might be recommended for you to ensure early detection and treatment.

In some cases, genetic testing can show that you are at no higher risk for developing a cancer than the average person,” she said.

Should You Consider Genetic Testing for Colon Cancer?

According to the Centers for Disease Control and Prevention (ÇDC), genetic testing will be recommended if:

• Your tumor screening results (IHC or MSI) are abnormal
• You have had colorectal cancer
• You had uterine - endometrial cancer - before age 50
• You have had multiple primary cancer diagnoses
• Several family members have had cancers related to Lynch syndrome
• You have a family member with Lynch syndrome or other hereditary colorectal syndromes.

While most diagnosed colon cancers are sporadic – meaning a colorectal cancer patient has no family history of the condition and the cancer is more likely to form after age 50 – some 5-10% of people with colon cancer have a hereditary form where they have inherited a genetic risk from one of their parents. As a result, the chance of developing colon cancer is 50% greater than the average person. These inherited colorectal syndromes include familial adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer, also referred to as Lynch Syndrome.

Inherited Colorectal Syndromes: Lynch Syndrome and FAP

Lynch Syndrome

Lynch Syndrome, the most common genetic syndrome associated with colorectal cancer, is caused by a failure of cellular DNA repair genes that produce many gene mutations. People with Lynch Syndrome have parents, children, sisters and brothers, as well as other close relatives, who have a 50% risk of having this condition. About 3% of colorectal cancer cases are the result of Lynch Syndrome. People with Lynch Syndrome need more frequent screening.

Familial Adenomatous Polyposis (FAP)

The second-most common form of hereditary colorectal cancer is familial adenomatous polyposis (FAP), which results in the growth of hundreds to thousands of benign (non-cancerous) polyps in the colon and rectum. Overtime, these polyps can become cancerous at an average age of 39. FAP occurs in one in 10,000 people.

What Causes Colon Cancer?

Other risk factors that increase your risk for colorectal cancer include:

• Age, risk increases after age 50
• Alcohol, drinking 3 or more alcoholic beverages per day increases the risk of colorectal cancer
• Cigarette smoking
• Race, Black individuals have an increased risk of colorectal cancer and death compared to other races
• Overweight and obese
• Inflammatory bowel disease
• Personal history, including a previous colorectal cancer, high-risk adenomas (colorectal polyps that are 1 centimeter or larger in size or that have cells that look abnormal under a microscope), ovarian cancer, and inflammatory bowel disease
• Inactivity
• A diet rich in red meat

While you cannot reduce your genetic risk for colon cancer, there are some risks that can be alleviated, especially those that require a lifestyle change.

Make healthy choices by increasing physical activity, maintaining a healthy weight, limiting your alcohol consumption, avoiding tobacco, and eating a diet low in animal fats and high in fruits, vegetables and whole grains.

The Best Way to Reduce Your Risk

The most effective way to reduce your risk of colorectal cancer is routine screening, beginning at age 45, then continuing to get screened at regular intervals. However, your doctor may recommend testing earlier than 45 depending on your risk. Most colon cancers begin as precancerous polyps, which can be present in the colon for years before turning cancerous. You may have no symptoms, so screening is essential to find them before they turn into cancer.

If you believe you are at increased risk for colon cancer or are concerned about a hereditary risk, ask your doctor when you should begin screening and to recommend a genetic counselor to speak with.

Learn More About the Baystate Family Cancer Risk Program

Baystate Health offers genetic counseling and testing for people with a family history or personal history of cancer. Our goal is to provide the right test, to the right person, at the right time. Learn more.