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School of Medicine
How common is colon cancer?
Colorectal cancer is a major cause of death in western societies and in countries with diets high in animal fats and protein and low in fiber. It ranks as the third most common cancer in the United States below breast cancer and lung cancer. About 130,000 new cases are diagnosed each year in North America, and 56,000 die annually from this disease. Epidemiological studies have shown an increase in the incidence of colorectal cancer in both whites and non-whites with African Americans having a substantially increased risk of dying.
Is colon cancer preventable?
Colon cancer screening is one way that everyone can improve his or her chances against colon cancer. Early detection is essential to improve survival if cancer is found. Screening is vital to prevention and should be a part of routine care.
Current recommendations for colorectal cancer screening for asymptomatic average-risk individuals 50 years of age or older include: annual fecal occult blood test and sigmoidoscopy every five years, or colonoscopy every 10 years or double-contrast barium enema every 10 years. High-risk individuals (those with previous colon cancer, inflammatory bowel disease, or history of colorectal polyps) require surveillance colonoscopy every two to five years depending on the individual case. People with a family history of colorectal cancer should undergo screening colonoscopy starting at age 40, or 10 years before the youngest case in the family, which ever comes first. Environmental, dietary and genetic factors are thought to play a role in the development of colorectal cancer.
Does exercise help prevent colon cancer?
There have been several epidemiological studies that suggest sedentary lifestyle or decreased physical activity is associated with an increased risk of colorectal cancer. Though the mechanism for such a finding continues to be speculative, there is interesting data to support this theory. Studies have shown that shortened colonic transit times are associated with a lower incidence of colorectal cancer. Exercise is believed to shorten these transit times. Exercisers consume diets higher in fiber that are also associated with reduced transit time in the gut. In addition, fecal bile acids are present in the stool at lower concentration in individuals who exercise regularly. Colorectal cancer is also associated with obesity and elevated cholesterol levels which are reduced in populations who receive regular exercise.
What is the prognosis?
The prognosis of patients with colorectal cancer who undergo curative resection appears to correlate with the Duke’s stage. In Duke’s stage C, prognosis is greatly influenced by the number of positive lymph nodes found at surgery. Four or more positive nodes decrease the five-year survival rate, whereas three or fewer nodes impart a higher five-year survival rate (about 55 percent). Tumor histology also influences outcome. Tumors that are well differentiated have a better prognosis. Mucinous, scirrhous and signet ring cell cancer are considered more aggressive and are accompanied by a less favorable prognosis.
Is colon cancer treatable?
Yes. The treatment of choice for colorectal cancer is surgical resection. The goal is to remove the affected bowel with wide margins and also to remove the blood and lymphatic supply at the same time. Adjuvant chemotherapy has been shown to be effective in decreasing recurrence and the prolongation of disease free survival in patients with Duke’s stage C disease.
Is colon cancer inherited?
The most common risk factor for colorectal cancer is a positive family history. Approximately 20 percent of colorectal cancer cases are familial in origin. In fact, first-degree relatives of persons with colon cancer have been found to have a two- to three-fold increase risk of colorectal cancer compared with controls. About 5 percent of patients with colorectal cancer have clearly defined inherited syndromes such as familial adenomatous polyposis (FAP) and hereditary nonpolyposis colorectal cancer (HNPCC). These syndromes are well described, both genetically and phenotypically, and are characterized by dominant inheritance, high penetrance, and high risk of colorectal cancer.
In cases of sporadic colorectal cancers, where no family history exists, an acquired point mutation on chromosome 5q21 has been identified (MCC gene). Oncogenes C-myc and Ras have been associated with colorectal cancers showing elevated C-myc levels in most cases of colorectal cancer and Ras point mutations found to be an early event in transformation of premalignant adenomas to colorectal cancers.