Colon Cancer: Overview and Symptoms

Colon cancer is the third most common cancer worldwide and the second most common cause of cancer death. It accounts for 10 percent of all cancer deaths in the United States.

It is a common and potentially lethal disease, with advanced cancers commonly spreading to the surrounding area and throughout the body, including the liver, lungs, and lymph nodes. However, colon cancer tends to grow slowly and is generally treatable for many years before it becomes advanced. Thus, regular screenings (see Diagnosis section) and early treatment of precancers and early cancers can drastically reduce the rate of life-threatening disease. In fact, regular screening for colon cancer is one of the most important - and life-saving - public health recommendations in the United States.

Symptoms

• Common symptoms include weight loss, weakness, fatigue, abdominal pain, a change in bowel habits, and decreased caliber of stool.
• Cancers of the right side of the colon may also cause melena (black stools) or a right-sided abdominal mass.
• Cancers of the left side of the colon may result in constipation, diarrhea, and hematochezia (bleeding from the rectum). These patients are also at much higher risk of intestinal obstruction, with symptoms that include nausea, vomiting, absence of bowel movements and flatus, and abdominal distension. 

Risk Factors

• Age: About 90 percent of cases occur in people over age 50, and incidence increases with age.
  
• Family history: Approximately 25 percent of patients have a positive family history. There is an increased risk if one or more first-degree relatives has colon cancer.
  
• Tobacco use
  
• Excessive alcohol use
  
• Coexisting diseases of the colon: Ulcerative colitis and Crohn's disease increase the risk of colon cancer. There appears to be a higher risk with ulcerative colitis (as much as a five-fold to 15-fold increased risk) than with Crohn's disease.
  
• Excess weight: People who are mildly or moderately obese appear to have a 10 to 35 percent greater risk. Severely obese persons (body mass index greater than 40) have a 45 percent greater risk.
  
• In contrast to these risk factors, certain dietary patterns and increased physical activity are associated with reduced colon cancer risk. Refer to Nutritional Considerations below.

Diagnosis

• History and physical examination should include a rectal exam and evaluation for occult rectal bleeding.
  
• Colonoscopy to visualize polyps or tumors is the most important test to diagnose colon cancers. It allows for biopsy of the lesions and can also remove growths. Colonoscopy is the best screening test to identify pre-cancers and early cancers of the colon.  It is recommended once every 10 years in all individuals over age 50, and earlier in individuals with heightened risk for the disease. "Virtual colonoscopy" using CT scan or MRI is under investigation, but has not yet been proven reliable.
  
• When colon cancer is diagnosed, patients usually require further testing to determine whether the cancer has spread beyond the colon. These tests include blood testing and CT scans of the thorax, abdomen, and pelvis.
  
• Blood testing is also often used to identify various tumor markers, which help to determine prognosis and evaluate for disease recurrence.
  

Treatment

• Surgery to remove the cancer is the definitive treatment.
  
• Advanced cancers require chemotherapy in addition to surgical removal of the tumor. In some cases, particularly rectal cancers, radiation is also used.
  
• If the cancer has spread to other areas of the body, further treatment will be necessary. This may include surgery, chemotherapy, or other modalities. In addition, a new medication called Avastin has recently been approved by the Food and Drug Administration as a first-line treatment for metastatic disease.

Colon Cancer: Nutritional Considerations

In population studies, the following factors are associated with reduced risk of colon cancer:

• Avoiding or limiting meat consumption: Higher intake of processed red meat appears to increase the risk of colon cancer. This may be due to the presence of nitrosamines and polycyclic aromatic hydrocarbons, which are suspected carcinogens.
  
  In the European Prospective Investigation into Cancer and Nutrition (EPIC) study, individuals who ate at least 160 grams per day of red or processed meat had a 70 percent greater risk for colorectal cancer. In the Cancer Prevention Study II (CPS II), individuals who ate the highest amount of red meat and processed meat were at 50 percent greater risk for colon cancer and a 70 percent increased risk of rectal cancer.
  
  Although white meat may carry a lower risk than red meat, a study of Seventh Day Adventist men found that eating white meat more than once per week was associated with more than three times the risk compared with people who abstained from eating white meat.
  
  Further, the high cholesterol contained in animal products may increase the risk of colon cancer.
  
  In contrast, plant-based and vegetarian diets are associated with lower incidence of colon cancer, probably due to the absence of meat and to the inclusion of protective plant constituents, as explained below.
• Avoiding or limiting alcohol use: Several studies show that alcohol consumption (at least one drink per day) is independently associated with the risk of colon cancer.
• Increased fiber intake: Studies on dietary fiber and colorectal cancer risk have yielded conflicting findings. Some studies show that fiber reduces the risk of colon polyps, which are precancerous growths. However, a recent study found that the reduction in risk associated with high dietary fiber intake was small.
• B vitamins may reduce the risk of colon cancer: Folic acid, found in leafy green vegetables, beans, and whole grains, plays an important role in the maintenance of DNA, the genetic material inside our cells. Some evidence suggests that individuals who eat the most folate have as much as a 40 percent lower risk for colon cancer.
  
  Similarly, vitamin B6 is involved in DNA processes and other important body functions. Studies have shown that individuals who consume the highest amounts of vitamin B6 may have a reduced risk for colon cancer. Healthful sources include beans, nuts, legumes, whole grains, and fortified breads and cereals.
• Vitamin E may reduce the risk of colon cancer: Evidence has suggested that eating one-fourth of an ounce of nuts per day - an excellent source of vitamin E - may protect against colon cancer, particularly in women. The lower risk is attributable to food sources of vitamin E, but not vitamin supplements. Higher intakes of vitamin E - rich foods, such as nuts, seeds, and wheat germ, appear to reduce risk significantly in people younger than 65.
• Calcium and vitamin D may reduce the risk of colon cancer: Higher intakes of both calcium and vitamin D are associated with lower risk for colorectal cancer and may decrease the risk of recurrence. A lower risk for colon cancer has been found in persons who ingested 700 mg per day of calcium, compared with those who have lower intakes; however, higher intakes did not increase the benefit.