Understanding Colon Cancer Causes and its Key Risk Factors

What is colon cancer?

Colon cancer is often a slow developing cancer¹ that grows in the large intestine, typically over many years. Its precursors are abnormal cell growths in the intestine called polyps, either with stalks or without them.

Because the rectum is also a part of the large intestine, colon and rectal cancer are often grouped together and referred to as colorectal cancer in the medical community.

Just over 4%² of people in the U.S. will be diagnosed with colorectal cancer in their lifetime. The disease will account for just under 8% of all cancer in the U.S. in 2021. This makes it the fourth-most diagnosed³ cancer behind breast, lung, and prostate cancers.

Understanding colon cancer causes and risk factors

While colon cancer affects men and women of all races and ethnicities, some common causes and risk factors are associated with the disease. Let's look at the main colon cancer risk factors, including genetics, health, demographics, and lifestyle.

Genetic factors

A key mutation of the 'APC' gene

The adenomatous polyposis coli (APC) gene codes for a protein that is responsible for tumor suppression.

People with a condition called familial adenomatous polyposis⁴ (FAP) have a mutation of this gene that lowers its ability to suppress tumors and increases the risk of intestinal polyps developing into colorectal cancer.

There are a few forms of FAP, and about 80% of people who test positive for this mutation develop the condition.

Lynch disease

Like FAP, Lynch syndrome⁵ is caused by genetic mutations, but in this instance, the mutations negatively affect the repair of DNA mismatches. This condition accounts for about 4,000 cases of colon cancer annually.

Other inherited conditions

Juvenile polyposis syndrome⁶, Peutz-Jeghers syndrome⁷, and MUTYH-associated polyposis⁸ can also increase your risk of the disease. These and other inherited conditions like FAP and Lynch disease account for about 5% of colon cancer⁹.

Health conditions

Inflammatory bowel disease (IBD)

IBD conditions such as Crohn's disease and ulcerative colitis can lead to chronic inflammation of the large intestine. Anti-inflammatory treatments have been shown¹⁰ to decrease this risk, and only about one percent of colon cancer is attributed to IBD.

Metabolic disorders

People with obesity, type II diabetes, and high cholesterol levels appear to have a higher risk of colon cancer.

Abnormal polyps

Precancerous polyps known as adenomas¹¹ can form in the mucous membrane of the large intestine. People with multiple or larger adenomas have an increased risk¹² for colon cancer.

Key demographics

Age

About 90 percent¹³ of colon cancer cases are diagnosed in people aged 50 and older. However, the rate of the disease has been increasing for people under age 55.

Race

African Americans have higher rates of colon cancer than any other ethnic group in the U.S. and are more likely to be diagnosed at a younger age. Although the hereditary risk isn't greater¹⁴, the risk of contracting non-hereditary colon cancer (which makes up 95% of cases) is at least 20% greater¹⁵.

Family history

Those with a family history¹⁴ of colorectal cancer are more likely to be diagnosed with the condition, especially if they have close relatives who received their diagnosis when they were under 60. The risk also increases if a person has had colorectal cancer in the past.

Lifestyle factors

Diet

According to Cancer.gov¹⁶, there is a large body of research linking red and processed meat to DNA damage, which leads to the development of colorectal tumors. The International Agency for Research on Cancer¹⁷ (IARC) listed processed meat as a carcinogen (cancer causer) in 2015.

A high-fat¹⁸, low fiber diet¹⁹ can also increase the risk of getting colorectal cancer.

Drinking alcohol and smoking tobacco

In 2009, the IARC found that smoking causes colorectal cancer¹² and increases the risk of developing the disease by about 50% compared to those who have never smoked. Heavy alcohol consumption has also been shown to increase the risk by about 25%.

Obesity

Obesity affects men's risk for colorectal cancer¹² much more than it does women's:

• Women who are obese have about a 10% greater chance of developing colon cancer but have no increased risk for rectal cancer.

• Men who are obese have a 50% greater chance of developing colon cancer and a 25% greater chance of developing rectal cancer.

Sedentary lifestyle

The least active people have been shown to have a 25%-50% greater risk¹² for developing colon cancer than the most active people.  However, rectal cancer rates don't seem to be affected by a low-activity lifestyle.

The importance of early diagnosis and screening 

Because the rates of colon cancer have been on the rise in people under the age of 50, the American Cancer Society recommends that everyone aged 45 and over get screened annually. This is especially important for African Americans, who are more likely to be diagnosed at a younger age.

If you have a family history of FAP, Lynch syndrome, or colorectal cancer, it's important to let your healthcare practitioner know right away because the disease may manifest even earlier. For instance, 39 is the average age when people with the main form of FAP develop colon cancer.²⁰

Initial testing

Your healthcare provider can provide a blood test to determine if you may have certain gene mutations associated with colon cancer.

If no genetic factors are suspected, a stool test may be requested instead. According to the CDC, you can typically do these gFOBT, FIT, and FIT-DNA tests in the comfort of your home then send them to the lab for analysis.

Colon cancer diagnostic tests

If indicators are present in the initial test, the most common screening tool is a colonoscopy. This is a scope inserted into the rectum to view the intestinal lining and remove any polyps. This is typically done every ten years.

Some alternatives to a colonoscopy include a flexible sigmoidoscopy, which is a shorter scope for viewing the rectum and the lower third of the colon. Since this isn't as thorough, it's recommended to have this exam every five years.

A "virtual" colonoscopy known as a CT colonography²¹ can also be conducted to view the digestive system using computer graphics and x-rays to detect any growths or polyps using 3–D imaging. This is the least invasive of the three options.

Protecting yourself from colon cancer

1. Know the signs

One of the most challenging aspects of colon cancer is that there are often no signs and symptoms before diagnosis, or they are attributed to other factors. This is another reason why early screening is so beneficial.

For people who do have symptoms, changes include:

• Blood in the stools

• Lower back pain, bloating, and cramps

• Unexplained weight loss 

• Fatigue

• More frequent bowel movements

• Anemia

2. Adopt essential health habits

Limit red and processed meats

Since both red and processed meat can potentially cause cancer, diets low in these foods are best. Experts say that completely eliminating them²² from your meal planning is even better. Poultry, fish, beans, and legumes are some healthy options to replace your red meat servings.

Exercise regularly

The American Cancer Society²³ (ACS) advises that you try to fit in about 150-300 minutes of moderate-level activity per week, or 75-150 minutes of more intense exercise.

Maintain a healthy body weight

To keep your weight at a healthy level, reduce your intake of saturated animal fats and eat omega-3 rich foods like salmon, flax seeds, and walnuts instead.  The ACS also suggests having about 1-2.5 cups of fruit and 1-4 cups of vegetables²⁴ daily.

Avoid smoking and limit alcohol consumption

Because of the link between smoking and colon cancer, quitting smoking is one of the most effective ways to ensure that you stay healthy and help prevent colon cancer.

In addition, non-drinkers have the lowest risk of getting the disease. Those who limit their consumption of alcoholic beverages have improved outcomes compared to moderate to heavy drinkers.

3. Understand your treatment options

One of the main treatments²⁵ for early-stage colon cancer is the removal of both precancerous and cancerous polyps during colonoscopies and sigmoidoscopies. For polyps that have cancer cells at their edges, further surgery may be recommended.

As colon cancer advances, parts of the colon may be removed and reconstructed, and radiation and chemotherapy are administered to increase your chances of positive outcomes.

Targeted²⁶ therapies that have undergone clinical trials may also be added to your treatment plan, usually in cases of advanced disease. Immunotherapy has a role in selecting patients with colon cancer.