How is colorectal cancer screened and diagnosed?
Colorectal cancer usually is diagnosed by a sigmoidoscopy or colonoscopy. In these tests, a flexible viewing tube is inserted into your rectum and colon to look for polyps or cancerous masses. You also may have a test called a barium enema. In this test, a fluid containing a substance called barium is pumped into your rectum before X-rays are taken. The barium helps
abnormalities show up on the X-rays. These tests provide information about the size and location of the cancer. Colorectal cancer can take many years to develop and early detection of colorectal cancer greatly improves the chances of a cure. Therefore, screening for the disease is recommended in individuals who are at increased risk. There are several different tests available for this purpose.
Digital rectal exam (DRE): The doctor inserts a lubricated, gloved finger into the rectum to feel for abnormal areas.
Fecal occult blood test (FOBT): A test for blood in the stool.
Sigmoidoscopy: A lighted probe (sigmoidoscope) is inserted into the rectum and lower colon to check for polyps and other abnormalities.
Colonoscopy: A lighted probe called a colonoscope is inserted into the rectum and the entire colon to look for polyps and other abnormalities that may be caused by cancer. A colonoscopy has the advantage that if polyps are found during the procedure they can be immediately removed. Tissue can also be taken for biopsy.
Double contrast barium enema (DCBE): An enema containing barium, which helps the outline of the colon and rectum stand out on X-rays, is given to the patient. The doctor then takes a series of X-rays of the colon and rectum.
Virtual colonoscopy can image the colon using x-rays and is approaching colonoscopy in senstivity for polyps. However, any polyps found must still be removed by standard colonoscopy.
Computed axial tomography is an x-ray method that can be used to determine the degree of spread of cancer, but is not sensitive enough to use for screening. Some cancers are found in CAT scans performed for other reasons.
Blood tests: Measurement of the patients blood for elevated levels of certain proteins can give an indication of tumor load. In particular, high levels of carcinoembryonic antigen CEA in the blood can indicate metastasis of adenocarcinoma.