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Incidence, Risk Factors and Screening
Carcinoma of the colon and rectum is the 2nd most common cause of cancer death in the United States. This disease has several known risk factors, including age, history of inflammatory bowel disease, low fiber diet, family history, and smoking. People over the age of 50 are recommended to get regular screening, consisting of colonoscopy, flexible sigmoidoscopy, and/or fecal occult blood test. There are several familiar disorders associated with higher incidence of this disease.
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The initial lesion on the colonic epithelial is a polyp, which is a noncancerous growth arising from the mucosal layer. Polyps are classified as juvenile, hyperplastic, or adenomatous. Only the adenomatous polyps are known to progress to a malignancy, and only a small portion of these polyps develop into a carcinoma. Many people have adenomatous polyps that never progress to a malignant condition. Approximately 30% of middle-aged adults and 50% of elderly adults have polyps, but less than 1% of these polyps progress to a carcinoma. Polyps are usually asymptomatic, but may produce blood. Polyps may progress to a malignant tumor due to a number of specific DNA mutations in cancer-related genes.
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Signs and Symptoms
Generally, colorectal adenocarcinoma grows slowly and may be asymptomatic for a number of years. When symptoms arise, they may include blood in the stool (either microscopically or visibly), iron deficiency anemia due to chronic blood loss, fatigue, weakness, bowel obstruction, and changing bowel habits. The pattern of symptoms largely depends on the portion of the bowel that is affected.
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Diagnosis and Treatment
The presence of a malignant tumor in the bowel can be confirmed by colonoscopy, which can serve as both a diagnostic and prevention modality. Polyps found during routine screening are removed, thereby halting any potential progression to a malignancy. Malignant tumors can be biopsied and staged during colonoscopy. The standard treatment is surgical resection of the affected section of bowel, perhaps in conjunction with chemotherapy and/or radiation in advanced disease or in the case of metastasis.
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Colon cancer survivability depends on the stage of the disease. Stage 1 is contained to the large intestine or rectum and has a 5-year mortality rate of 5-10%. Stage 2 has spread beyond the bowel and has a mortality rate of 15-30%. Stage 3 has spread to the lymph nodes and mortality ranges from 30-75%, depending on the number of lymph nodes involved. Stage 4 involves distant metastasis and has greater than 95% mortality. Patients are fairly evenly spread throughout the 4 stages at the time of diagnosis.
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Cornett Patricia A, Dea Tiffany O, "Chapter 39. Cancer" (Chapter). McPhee SJ, Papadakis MA, Tierney LM, Jr.: CURRENT Medical Diagnosis & Treatment 2010
Mayer Robert J, "Chapter 87. Gastrointestinal Tract Cancer" (Chapter). Fauci AS, Braunwald E, Kasper DL, Hauser SL, Longo DL, Jameson JL, Loscalzo J: Harrison's Principles of Internal Medicine, 17