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Colorectal Cancer: Overview and Risk Factors

Colon cancer is the third most common malignancy worldwide and the second leading cause of cancer-related mortality. It accounts for 10% of cancer deaths in the United States. Although the disease is common and often lethal, risk is reduced with regular screenings and timely removal of precancerous lesions, and possibly through dietary modifications. Some evidence also suggests that diet may influence the likelihood that precancerous lesions will become cancerous.

More than 95% of colon cancers are adenocarcinomas, which originate from glandular tissue. Presenting symptoms and complications depend on the location of the tumor. General symptoms include abdominal pain, a change in bowel habits, decreased caliber of stool, and constitutional symptoms, such as weight loss, weakness, and fatigue. Right-sided tumors may additionally present with melena or occult bleeding and a right-sided abdominal mass. Left-sided tumors may cause constipation, diarrhea, and, especially with distal left-sided and rectal tumors, hematochezia. Further, patients with left-sided tumors are at much higher risk of intestinal obstruction, which may present with nausea/vomiting, absence of bowel movements and flatus, and abdominal distension.

Local spread and distant metastases are common. Between 15% and 20% of patients diagnosed with colon cancer initially present with metastases, most commonly of the regional lymph nodes, liver, lungs, and peritoneum.

Risk Factors

The following factors are associated with increased risk for colorectal cancer:

Age. About 90% of cases occur in patients over 50 years of age, and incidence increases with age.

Family history. Approximately 25% of patients have a positive family history. Risk increases several-fold if one or more first-degree relatives have colon cancer.

Environment. Incidence is highest in developed countries. Those who migrate from regions of low incidence to regions of high incidence eventually assume a risk similar to that of their adopted countries. These associations may be attributable to diet (see Nutritional Considerations ).

Tobacco use.

Alcohol use (see Nutritional Considerations for more information).

Hereditary syndromes. These include Lynch syndrome and familial polyposis syndromes.

Inflammatory bowel disease. Both ulcerative colitis and Crohn's disease predispose to colon cancer. There appears to be a higher risk with ulcerative colitis (as much as a 5-fold to 15-fold increased risk) than with Crohn's disease.

Excess weight. Overweight is associated with colon cancer risk.1 Mildly and moderately obese individuals appear to have about 10% to 35% greater risk, respectively, compared with those who are at a healthy weight (BMI 18.5-24.9). Severely obese persons (BMI >40) have a 45% greater risk for colorectal cancer.2

In contrast to the above factors, increased physical activity is associated with reduced colon cancer risk. The presumed mechanisms are reduction in weight or in blood concentrations of insulin or insulin-like growth factor.


Colorectal Cancer: Diagnosis and Treatment >>