Cancer: Colon cancer
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Colon cancer is cancer of the large intestine (colon), the lower part of your digestive system. Rectal cancer is cancer of the last 6 inches of the colon. Together, they're often referred to as colorectal cancers.
Most cases of colon cancer begin as small, noncancerous (benign) clumps of cells called adenomatous polyps. Over time some of these polyps become colon cancers.
Polyps may be small and produce few, if any, symptoms. Regular screening tests can help prevent colon cancer by identifying polyps before they become cancerous. If signs and symptoms of colon cancer do appear, they may include changes in bowel habits, blood in your stool, persistent cramping, gas or abdominal pain.
What are the symptoms of Colon cancer?

Many people with colon cancer experience no symptoms in the early stages of the disease. When symptoms appear, they'll likely vary, depending on the cancer's size and location in your large intestine.
Signs and symptoms of colon cancer include:
  • A change in your bowel habits, including diarrhea or constipation or a change in the consistency of your stool for more than a couple of weeks
  • Rectal bleeding or blood in your stool
  • Persistent abdominal discomfort, such as cramps, gas or pain
  • Abdominal pain with a bowel movement
  • A feeling that your bowel doesn't empty completely
  • Weakness or fatigue
  • Unexplained weight loss
Blood in your stool may be a sign of cancer, but it can also indicate other conditions. Bright red blood you notice on bathroom tissue more commonly comes from hemorrhoids or minor tears (fissures) in your anus, for example. In addition, certain foods, such as beets or red licorice, can turn your stools red. Iron supplements and some anti-diarrheal medications may make stools black. Still, it's best to have any sign of blood or change in your stools checked promptly by your doctor because it can be a sign of something more serious.

Risks and causes of colon cancer:
Factors that may increase your risk of colon cancer include:
  • Age. About 90 percent of people diagnosed with colon cancer are older than 50. Colon cancer can occur in younger people, but it occurs much less frequently.
  • A personal history of colorectal cancer or polyps. If you've already had colon cancer or adenomatous polyps, you have a greater risk of colon cancer in the future.
  • Inflammatory intestinal conditions. Long-standing inflammatory diseases of the colon, such as ulcerative colitis and Crohn's disease, can increase your risk of colon cancer.
  • Inherited disorders that affect the colon. Genetic syndromes passed through generations of your family can increase your risk of colon cancer. These syndromes cause only about 5 percent of all colon cancers. One genetic syndrome called familial adenomatous polyposis (FAP) is a rare disorder that causes you to develop thousands of polyps in the lining of your colon and rectum. People with untreated FAP have a greater than 90 percent chance of developing colon cancer by age 45. Another genetic syndrome, hereditary nonpolyposis colorectal cancer (HNPCC), also called Lynch syndrome, is more common than FAP. People with HNPCC have an increased risk of colon cancer and tend to develop colon cancer at an early age. Both FAP and HNPCC can be detected through genetic testing. Talk to your doctor about whether your family history suggests you have a risk of these conditions.
  • Family history of colon cancer and colon polyps. You're more likely to develop colon cancer if you have a parent, sibling or child with the disease. If more than one family member has colon cancer or rectal cancer, your risk is even greater. In some cases, this connection may not be hereditary or genetic. Instead, cancers within the same family may result from shared exposure to an environmental carcinogen or from diet or lifestyle factors.

  • Diet. Colon cancer and rectal cancer may be associated with a diet low in fiber and high in fat and calories. Research in this area has had mixed results. Some studies have found an increased risk of colon cancer in people who eat diets high in red meat and processed meats.
    People who eat a diet similar to that of Western countries, such as the United States and Europe, have a higher risk of developing colon cancer than do people who eat diets typically seen in developing countries. When people move from a developing country to a Western country and adapt to the Western diet, their risk of colon cancer increases. Although many studies have tried to identify what part of the Western diet may cause colon cancer, the answer remains unknown.
  • A sedentary lifestyle. If you're inactive, you're more likely to develop colon cancer. This may be because when you're inactive, waste stays in your colon longer. Getting regular physical activity may reduce your risk.
  • Diabetes. People with diabetes and insulin resistance may have an increased risk of colon cancer.
  • Obesity. People who are obese have an increased risk of colon cancer and an increased risk of dying of colon cancer when compared with people considered normal weight.
  • Smoking. People who smoke cigarettes may have an increased risk of colon cancer. They may also have an increased chance of dying of colon cancer.
  • Alcohol. Heavy use of alcohol may increase your odds of colon cancer.
  • Growth hormone disorder. Acromegaly, an uncommon disorder that causes an excess of growth hormone in your body, may increase your risk of colon polyps and colon cancer.
  • Radiation therapy for cancer. Radiation therapy directed at the abdomen to treat previous cancers may increase the risk of colon cancer.
If you notice any symptoms of colon cancer, such as blood in your stool or a persistent change in bowel habits, see your doctor as soon as possible. Keep in mind that colorectal cancer can occur in younger as well as older people. If you're at high risk, don't wait until symptoms appear. See your doctor for regular screenings.
Talk to your doctor about when you should begin screening for colon cancer. Guidelines generally recommend colon cancer screenings begin at age 50. Your doctor may recommend more frequent or earlier screening if you have other risk factors, such as a family history of the disease.