Colon cancer is a cancer of the digestive system that starts in the colon (part of the large intestine). It shares many similarities with rectal cancer and the two cancers are commonly referred to as colorectal cancers. In most cases, colorectal cancers develop slowly over many years and are treatable if diagnosed early; regular screening for colon cancer is critical.
Not including skin cancers, colon cancer is the third-most-common cancer in the United States. It is just as common among women as among men. The lifetime risk of contracting colorectal cancer is approximately 1 in 20. Over 90 percent of cases occur after the age of 50.
Over 95 percent of colon and rectal cancers are adenocarcinomas, meaning that they start in the cells lining the inside of the colon or rectum. Most colorectal cancers begin as a polyp – a growth of tissue on the lining of the colon or rectum that grows outward towards the center. Not all polyps are dangerous, but the type known as an adenoma may become cancerous unless removed.
The relationship between diet, exercise, weight, and colorectal cancer is among the most pronounced of any type of cancer. A diet high in red meats, processed meats, and charred meats is known to increase the risk of colorectal cancer. Conversely, a diet low in such meats and high in fruits and vegetables lowers the risk. The benefits of high-fiber diets and vitamins/supplements have so far proven inconclusive.
Obesity, smoking, and alcohol consumption (more than two drinks per day for men and one per day for women) are linked to increased risk of colorectal cancer. Other risk factors include: having had polyps or previous colorectal cancer; a history of bowel disease, such as Crohn's or ulcerative colitis; a family history and genetic factors; and Type 2 diabetes.
Colon cancer often does not produce any symptoms until later in the disease, and many symptoms are also caused by non-cancerous factors. Symptoms include changes in bowel habits for more than a few days; feeling the need for a bowel movement even after having had one; rectal bleeding; cramping or abdominal pain; weakness and fatigue; and unexpected weight loss.
The best ways to prevent colorectal cancers are to control weight, diet, alcohol consumption, and to exercise frequently. For those with a family history of these cancers, genetic testing is available.
Screening is equally important. The death rate from colon and rectal cancers has been declining for two decades because of the prevalence of screening and early prevention. The American Cancer Society recommends that people at average risk for colon cancer have a screening test (colonoscopy or other type) beginning at age 50. The five-year survival rate for colon cancer now stands at about 90 percent when the cancer is found and treated early.
The primary treatment for colon cancer is surgery. The surgery can be through a traditional abdominal incision or, increasingly, through laparoscopic surgery, performed by specially-trained surgeons. Laparoscopic surgery uses several smaller incisions that heal faster and limit damage to the patient's immune system. Depending on the stage at which the cancer is detected, radiation and chemotherapy may also be options for colon cancer treatment.