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Colorectal cancer: Clinical
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Colorectal cancer or CRC is a malignancy that arises in the large intestines, which includes both the colon and rectum. It is the most common cancer of the gastrointestinal tract, and a major cause of death and disease around the world. Most colorectal tumors develop due to sporadic mutations, but some are caused by inherited conditions like familial adenomatous polyposis and Lynch syndrome.
Individuals at high-risk for CRC include those with inflammatory bowel disease, especially ulcerative colitis, hereditary colorectal cancer syndromes, such as familial adenomatous polyposis, and those with a family history of colorectal cancer or adenomatous polyps. Individuals at medium-risk for CRC include the elderly, and those that smoke, drink alcohol, eat red meat, and are obese. Finally, well established protective factors include a high-fiber diet full of fruits and vegetables.
Sometimes, especially early on, colorectal cancer is asymptomatic and it’s discovered by screening using either stool based tests or direct visualization. One stool based test is the guaiac-based fecal occult blood test or gFOBT which detects blood in the stool. Another test is fecal immunochemical test or FIT. This time instead of guaiac, there’s an antibody that attaches to any hemoglobin that’s present in the stool. Finally there’s the FIT-DNA test-which combines FIT with a test that detects genes associated with colorectal cancer in the stool, such as mutations in the adenomatous polyposis coli gene or APC gene. One direct visualization test is a colonoscopy, which is when a camera is inserted retrograde into the colon and rectum using a flexible tube and biopsies are taken. Another one is a flexible sigmoidoscopy, which uses a flexible tube to visualize the rectum and sigmoid colon. Finally, there’s CT colonography or a virtual colonoscopy- which is where CT scans are digitally assembled to produce 3-dimensional views of the colon.
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