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Colon cancer

Overview of colon cancer

Colon cancer, also called colorectal cancer, is cancer in the inner wall of the colon or rectum. Colon cancer is the third most common cancer in both men and women. The average American has about a 5 percent chance of developing colon cancer.

Our compassionate oncologists at Dignity Health provide expert treatment for colon cancer. Find a Doctor near you today for personalized care.


Screening finds many colon cancers early before symptoms even begin. Regular testing often prevents colon cancer from developing.

Symptoms of colon cancer include:

  • Changes in bowel activity, including diarrhea, constipation, or narrowing or inconsistency of the stool
  • Rectal bleeding
  • Feeling of incomplete emptying after a bowel movement
  • Bloody stool
  • Abdominal cramping or pain
  • Weakness or fatigue
  • Loss of appetite and weight loss

These symptoms appear similar to many other conditions, including hemorrhoids. See your doctor for the right diagnosis.


Cancer occurs when the DNA in cells mutate, causing cells to reproduce abnormally and grow out of control. Changes in cell growth can lead to tumors that spread throughout the body.

When these changes first happen in the cells lining the colon or rectum, the result is colon cancer. 

Like other cancers, experts still do not fully understand why some people develop colon cancer and others do not. However, there are risk factors, like a previous diagnosis of IBS, family history of colon cancer, and smoking.


The vast majority of colon cancers — 96 percent — are adenocarcinomas.

Adenocarcinoma cancers develop slowly, over 10 to 15 years. They start in the cells that make lubricating mucus for the colon and rectum. Before they become cancerous, they begin as noncancerous polyps in the lining of the colon or rectum. Your doctor can identify possible polyp growth during a colonoscopy.

Our skilled providers at Dignity Health provide personalized treatment for colon cancer. Find a Doctor near you.

Risk factors

Experts don’t yet fully understand what causes colon cancer. Certain risk factors increase your chances of developing it:

  • Personal or family history of colorectal polyps or cancer.
  • Genetics: 5 to 10 percent of colon cancers are related to genetic syndromes and mutations in genes. The most common type of inherited colon cancer is called Lynch syndrome (also known as hereditary non-polyposis colon cancer or HNPCC).
  • Personal history of inflammatory bowel disease, including ulcerative colitis and Crohn’s disease.
  • Type 2 diabetes.
  • 90 percent of colon cancers occur in people 50 and older.
  • African American race.

Lifestyle factors, such as smoking, obesity, not exercising, poor diet, and heavy alcohol use, may also increase the risk of colon cancer.


One of the best tools to prevent colon cancer is screening for people who do not have symptoms, as detecting colon cancer early offers the best chance of a cure.

Colon cancer takes a long time to develop and typically starts with observable signs that your doctor can identify. Precancerous “polyps” form in the colon as long as 10 years before these growths become cancerous.

If these polyps are found, your doctor can remove them to prevent colon cancer from developing. If some of the growths are cancerous, he or she can remove these cells before they spread.

As you get older, you should schedule regular appointments with your doctor – about once per year after the age of 45 – to screen for colon cancer. Your doctor may advise more frequent screenings if you’re at a higher risk of colon cancer from an inherited gene or condition like IBS or Crohn’s disease.

There are also lifestyle changes you can make to reduce your risk of all cancers:

  • Eating a diet that’s lower in processed red meats (such as hotdogs, lunch meat, and sausage) and higher in green leafy vegetables
  • Increasing your exercise and fitness level, as recommended by your doctor
  • Maintaining a healthy weight
  • Not smoking
  • Avoiding excess consumption of alcohol

The information contained in this article is meant for educational purposes only and should not replace advice from your healthcare provider.