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.
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.
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.