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Colonoscopy is the technique of choice for the diagnosis of colorectal cancer. The procedure involves a visual exploration inside the rectum and colon, and can be used to obtain tissue samples from any lesions for subsequent histological analysis (biopsy).
The colon must be flushed clean in preparation for the test by administering an evacuant the day before and/or on the day of the test. As the introduction of air into the colon, necessary to ensure it is distended correctly, causes discomfort and possibly pain, it is also a good idea to perform the colonoscopy under sedation.
The mortality associated with colonoscopies is 0.3 cases per 1.000 examinations. The rate of intestinal perforation or haemorrhage is 1–5 cases per 1000 procedures.
Degree of spread and staging of colorectal cancer
Whenever colon cancer is diagnosed, an assessment of how much it has spread should include an abdominal CT scan and a plain film chest X-ray. If the diagnosis is for rectal cancer, then a pelvic MRI scan is required as part of a locoregional assessment and a chest/abdominal CAT scan to study any distant metastasis. If the CAT scan reveals small hepatic lymph nodes suspected of metastasis, a liver MRI may help characterise and determine the number of lesions.
Regarding tumour markers, lactate dehydrogenase (LDH) and carcinoembryonic antigen (CEA) concentrations in blood must be determined once the diagnosis of colorectal cancer has been confirmed and before starting any treatment. The latter marker provides valuable prognostic information and is very useful throughout patient follow-up as high levels of CEA after cancer resection can be a sign of recurrence. However, it is important to emphasise that the CEA test cannot be used in either the diagnosis or screening of colorectal cancer.