Causes and Risk Factors of Colon Cancer

Colon cancer is the third leading cause of cancer-related deaths in the United States in both men and women. Most cancers in the colon develop from polyps, which are growths that form within the inner lining of the colon. While most polyps do not actually turn into cancer, the ones that are most likely to are called adenomatous polyps or adenomas. Large polyps (greater than one centimeter), polyps that contain abnormal cells (called dysplastic polyps), and having two or more polyps within the colon also increases the likelihood for colon cancer.

In terms of risk factors, a person's chance of developing colon cancer increases as he or she gets older, especially after the age of 50. Furthermore, having type 2 diabetes or inflammatory bowel disease (for example, ulcerative colitis), or a family history of colon cancer also increases a person's risk for developing the disease, as do some modifiable risk factors like being overweight and eating a diet rich in red and processed meats.

In the end, knowing the causes and risk factors for colon cancer can help you understand the importance of routine screening for colon cancer, as well as learn if you are one of the people who should begin screening at an earlier age.

Common Risk Factors

There are a number of factors that increase a person's risk for developing colon cancer, some within a person's control (considered modifiable) and some not, like age, ethnicity, and race, or genetics.

Age

Age is the number one risk factor for colon cancer.

According to the Centers for Disease Control and Prevention (CDC), more than 90 percent of colon cancer cases occur in people who are 50 years of age or older.

That said, young adults can get colon cancer too. In fact, the incidence of colon cancer in young people aged 15 to 39 is increasing, and experts are not sure why.

Moreover, contrary to popular thought, most colon cancers in young people are not linked to genetic syndromes, but occur sporadically.

The bottom line here is that while increasing age is a major risk factor for developing colon cancer, it's really important for anyone of any age to be familiar with the symptoms and risk factors (besides age) of this disease. 

Ethnicity and Race

Ethnicity is also a well-known factor associated with cancer risk. African Americans are more likely to develop and die from colon cancer than Caucasians. Another high-risk group for getting colon cancer are people of Jewish eastern European descent.

Being Overweight or Obese

The link between colon cancer and obesity is strong. All told, people who are obese are over 30 percent more likely to develop this type of cancer than people of normal weight. The good news is that in your journey to lose weight, regular physical activity can actually protect you from developing colon cancer.

Type 2 Diabetes

Research has consistently shown a link between type 2 diabetes and the development of colon cancer, and this link exists independent of diet or being overweight.

Personal History of Colonic Polyps

The term colon polyp refers to an abnormal growth in the lining of the colon.

 Most commonly, cancers of the colon develop from adenomatous polyps, with adenocarcinoma being the most prevalent type of colorectal tumor. Adenomatous polyps can be villous (frond or leaf-like), raised, or flat.

Virtually all colon cancers develop from adenomatous polyps; having one or more adenomatous polyps increases your risk of developing colon cancer. This risk is even higher the larger the polyp, the more polyps you have, and whether the polyp show dysplasia, meaning it contains some abnormal-looking cells.

The upside is that when these polyps are found and removed via colonoscopy, they no longer have the opportunity to transform from precancerous to cancerous.

Personal History of Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is characterized by conditions such as ulcerative colitis and Crohn's disease. Both are associated with the development of colon cancer, and disease duration is a major risk factor for identifying who (with IBD) is most at risk. 

For example, while the results of different studies vary slightly, according to one large study, the risk of colon cancer for people with ulcerative colitis was found to be 0.7 percent at 10 years, 7.9 percent at 20 years, and 33.2 percent at 30 years. 

In addition to disease duration, people with more extensive colitis (colon inflammation) are at a higher risk. More specifically, people whose entire colon is diseased (called pan-colitis) have the highest risk of developing colon cancer.

It's important to note that IBD should not be confused with irritable bowel syndrome (IBS), which does not increase a person's risk of developing colon cancer.

Radiation

Radiation to the abdomen, pelvis, or spine as a child increases the risk of developing colon cancer. This is why the Children's Oncology Group recommends colonoscopy every five years (starting at age 35 or 10 years after the treatment, whichever is later) for people who received a significant amount of abdominal pelvic and/or spinal radiation in their younger years.

Research also suggests that men who have received radiation therapy to treat prostate and testicular cancer have a higher rate of colon and rectal cancer (the rectum is the digestive tube located between the colon and anus).

Genetics

Research has shown that one in four cases of colon cancer has some sort of genetic link. So if you have a first-degree family member (brother, sister, father, mother, child) with colon cancer or polyps, your risk of developing colon cancer is increased. 

It's important to note that colon cancer runs in families, but these cancers are related to specific genetic syndromes only some of the time.

Familial Adenomatous Polyposis Syndrome (FAP)

This is a family-inherited syndrome that causes the development of hundreds (even thousands) of pre-cancerous polyps in your colon. People with FAP have nearly a 100 percent chance of developing colorectal cancer, often by the age of 45. Although it is fairly rare, people with FAP can be diagnosed with colon cancer as early as their teens. FAP symptoms may include a  change in bowel habits, abdominal pain, or bloody stools (from large polyps).

Hereditary Nonpolyposis Colorectal Cancer Syndrome (HNPCC)

Also referred to as Lynch syndrome, this is a family-inherited condition that may increase your risk of developing colon cancer by as much as 80 percent. There are no outward symptoms of HNPCC, but genetic testing, a family history of colon cancer, and screening exams, such as a colonoscopy, will help your doctor diagnose this syndrome.

Peutz-Jeghers Syndrome (PJS)

This is an inherited condition that causes colon polyps that are more prone to becoming cancerous. PJS is not common, affecting between one and 25,000 to one and 300,000 people at birth.

PJS can be passed on to a child (50/50 chance) or developed sporadically for unknown reasons. Some symptoms associated with the syndrome, which are usually spotted at birth, include pigmented dark spotting on the lips or in the mouth, clubbing of the fingers or toenails, and blood in the stool.

Lifestyle Risk Factors

While it's easy to become overwhelmed by the non-modifiable risk factors for developing colon cancer, remember that overweight/obesity—a common factor in the development of colon cancer—is something you can have influence over. In addition, these risk factors are also within your control.

Alcohol Consumption

Alcohol is now considered one of the major risk factors for colon cancer, and the risk is directly linked to the amount of alcohol consumed. In fact, even moderate alcohol consumption may put a person at risk.

Dietary Factors

Diets high in fat and cholesterol, especially red meats (for example, beef, lamb, and pork), have been linked to colon cancer. Research has also found that eating more than an ounce and a half of processed meat per day, such as hot dogs and lunch meat, increases the risk of death due to colon cancer. 

While there are no "set in stone" guidelines for exactly how much red or processed meat you can consume to avoid increasing your colon cancer risk, the World Cancer Research Fund recommends consuming less than 500 grams of red meat per week (equivalent to about 17.5 ounces per week) and eating very little (if any) processed meats.

The American Cancer Society also recommends limiting red and processed meats (although there are no set consumption guidelines) and eating more fruits, vegetables, and whole grains to lower your risk for getting colon cancer. 

Smoking

According to a study in the Journal of the American Medical Association, ever-smokers are 18 percent more likely to develop colon cancer than someone who never smoked. Moreover, a person's risk of developing colon cancer increases proportionately with the number of years they smoke. The good news is that as soon as a person quits smoking, their personal risk of colon cancer starts to decrease.

Possible Links

There are many other factors linked to an increased risk of developing colon cancer, though it's important to note that the jury is still out on them. Some of these include:

• Long-term androgen deprivation therapy (ADT), possibly due to insulin resistance as a complication of ADT

• Removal of the gallbladder (cholecystectomy), which has been linked to increased risk of right-sided colon cancer

• Deficiency in vitamin D, also called the "sunshine vitamin" (your body makes it when exposed to ultraviolet rays)

• Certain medical conditions, like acromegaly or coronary heart disease

• Kidney transplant, due to long-term suppression of the immune system

More controversial (meaning the link or connection is even fuzzier) risk factors include:

• Elevated C-reactive protein (CRP) found in a person's bloodstream; CRP is a protein made in the liver that increases in response to inflammation in the body
• Chronic constipation and regular use of laxatives, especially non-fiber laxatives
• Infection with certain viruses or bacteria (for example, Helicobacter pylori infection)

Sources:

American Cancer Society. (2018). Colorectal Cancer Risk Factors. www.cancer.org/cancer/colon-rectal-cancer/causes-risks-prevention/risk-factors.html

Aykan NF. Red Meat and Colorectal Cancer. Oncol Rev. 2015 Feb 10;9(1):288.

Botteri E, Iodice S, Bagnardi V, Rajmondi S, Lowendels AB, Maisonneuve P. Smoking and colorectal cancer: a meta-analysis. JAMA. 2008 Dec 17;300(23):2765-78.

Centers for Disease Control and Prevention. (2016). What Are the Risk Factors for Colorectal Cancer? www.cdc.gov/cancer/colorectal/basic_info/risk_factors.htm

Children's Oncology Group. (2013). Long-Term Follow-Up Guidelines for Survivors of Childhood, Adolescent, and Young Adult Cancers. www.survivorshipguidelines.org/pdf/LTFUGuidelines_40.pdf​

Citronberg J, Kantor ED, Potter JD, White E. A prospective study of bowel movement frequency, constipation, and laxative use on colorectal cancer risk. Am J Gastroenterol. 2014 Oct;109(10):1640-49.

Desautels D, Czaykowski P, Mugent Z, Demers AA, Mahmud SM, Singh H. Risk of colorectal cancer after the diagnosis of prostate cancer: A population-based study. Cancer. 2016 Apr 15;122(8):1254-60.

Kim ER, Chang DK. Colorectal cancer in inflammatory bowel disease: The risk, pathogenesis, prevention and diagnosis. World J Gastroenterol. 2014 Aug 7;20(29):9872-81.

Sinha R, Cross AJ, Graubard Bl, Leitzmann MF, Schatzkin A. Meat Intake, and Mortality: A Prospective Study of Over Half a Million People. Archives of Internal Medicine. 2009 169:562-71.

Swede H et al. Baseline serum C-reactive protein and death from colorectal cancer in the NHANES III cohort. Int J Cancer. 2014 Apr 15;134(8):1862-70.

World Cancer Research Fund and American Institute for Cancer Research. (2007). Food, nutrition, physical activity and the prevention of cancer: a global perspective. Washington DC: AICR; 2007.