Colon Cancer Risk Factors

By Dianne Lange. Medically reviewed by Tom Iarocci, MD. May 7th 2016

Most colon cancers first appear as benign polyps.

Although most polyps are harmless, 1 in 100 will become malignant, says Philadelphia physician Richard C. Wender, MD, chief cancer control officer of the American Cancer Society. The larger polyps with the most abnormal cells create the highest risk of becoming cancer, he says.

Why? It’s all about genetic mishaps.

“Cancer is a disease of genes,” says Wender. When something goes wrong with those snippets of DNA, cells refuse to die or grow out of control — or both. The pile-up of abnormal cells that becomes a polyp is only the beginning. When exposed to certain triggers, or “promoters,” the genes in those vulnerable cells undergo further mutations and become a cancer.  

In one study, researchers examining more than 13,000 genes found that cells from colon tumors had approximately 90 mutant genes on average, 69 of which were known to be involved in colorectal cancers (cancers of the colon or rectum).

Recently, scientists discovered yet another genetic mechanism — that is, certain “master switches” in areas once thought to have no purpose, termed junk DNA (i.e., DNA between genes), which turn primary genes associated with colon cancer on or off.

Risk Factors for Colon Cancer

Here are some of the risk factors for colon cancer, many of which can be avoided:

Aging: Genetic mutations tend to develop gradually, so more will accumulate the longer one lives. More than 90 percent of people with colon cancer are over 50 years old.

Inflammation: Infection by bacteria or viruses creates inflammation, which accounts for about 16 percent of new cancers worldwide, including colon cancer. The theory is that the flood of chemicals released as the immune system battles invaders will then damage the genetic material of healthy cells and interfere with the ability of those cells to repair themselves.

Wender explains that, although there are a number of theories, chronic inflammation is high on the list that is being investigated. Chronic inflammation with inflammatory bowel disease (IBD), Crohn’s disease and ulcerative colitis cause the release of DNA-damaging chemicals from immune cells, too. That may explain why 1 person in 10 with IBD does develop colon cancer.  

Obesity: “About 10 percent of colon cancers are related to obesity,” says Wender. Some researchers have targeted the fat hormone leptin as one likely culprit, because it increases blood supply to precancerous cells. Recently, a study revealed that men with high levels of leptin, high body mass indexes and large waistlines were more likely to develop polyps than were their thinner cohorts.

Sedentary lifestyle: More than 40,000 cases of colon cancer a year are attributed to lack of physical activity. Researchers have found a 25- to 30-percent lower risk of colon cancer among people who are physically active. Again, inflammation is the likely culprit, but the exact mechanism hasn’t been identified.

Drinking alcohol: Having three or more drinks a day increases colon cancer risk. Scientists suspect it’s because people who drink a lot tend to run low on folate, a nutrient that can protect against cancer.

Cigarette smoking: Research shows that people who smoke for a long time are at higher risk for colorectal cancer, even when all other risk factors — including family history — are eliminated. In one study, people who smoked for 40 years or longer had a 30-percent increased risk of developing colorectal cancer. (Smokers tend to have more colon polyps than normal, but removed growths are also more likely to recur in smokers.)

Unhealthy diet: Digesting red meat forms chemicals in the body that are toxic to genes. Processed meats, especially hot dogs, sausage and bacon, contain nitrites, which are converted to potentially carcinogenic chemicals. Studies show that the more red meat you eat, the higher your risk of developing colon cancer.

Inheriting Colon Cancer

About 70 percent of the 96,830 colon cancers diagnosed each year are said to be sporadic because there is no prior family history. However, if your parent or sibling had colon cancer, it’s no longer sporadic — you have a family history.

  • Up to 30 percent of cancer cases arise in people who have this familial risk.

If you have a first-degree relative (parent, sibling or child) who developed colon cancer at a young age, talk to your health-care provider about whether you have inherited the genetic “promoter” or switch that may lead to cancer. If you have, you are at a very high risk of developing the disease and need specific, early screening to detect the disease.

Early Symptoms of Colon Cancer

Be alert to symptoms of colon cancer that may a prompt early diagnosis and treatment, says Wender. If you notice any of the following, call your health-care provider for an examination, no matter how recent your last colonoscopy:

  • A change in usual bowel movements, including diarrhea, constipation or narrow stool, that lasts for more than six days;
  • A persistent change in the consistency of your stool;
  • Feeling that your bowel hasn't completely emptied after a bowel movement;
  • Rectal bleeding;
  • Blood in your stool
  • Unexplained weight loss;
  • Persistent abdominal discomfort, such as cramps, gas or pain; and
  • Nausea and vomiting.

Next Steps

  • The good news is that, over the last 10 years, the incidence rate of colon cancer has fallen 30 percent in people over 50 years old, according to the American Cancer Society. Deaths from colon cancer have also declined, falling about 3 percent per year over the last decade. The decline may be due to more people being screened and more suspicious polyps being removed.
  • New research suggests that simply sitting for a long time without a break may boost cancer risk — even among those who exercise regularly. In addition to getting screened annually, make leisure time more dynamic by adding gardening, bowling or biking to your activity regimen.

For Caregivers

If you’re taking care of a loved one at high risk for colon cancer, you can inspire them to healthier habits by also quitting smoking, lowering the bad cholesterols in a fatty diet, exercising more and watching your own body weight. You both need to need to avoid habits and behaviors that promote cancer. 

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