Colorectal cancer is cancer that originates in the large intestine (colon) or rectum. Colorectal cancer may be found because a patient is having gastrointestinal symptoms, such as abdominal pain and bloody stools, that cause doctors to examine the large intestine, or cancer may be found during a colonoscopy for cancer screening. “Red flag” symptoms are not present in all cases of colorectal cancer, especially in the early stages when the cancer is most treatable.
One diagnostic procedure for visualizing colon cancer is a colonoscopy. In a colonoscopy, the patient is sedated and a flexible tube with a lighted camera on it is threaded into the colon. The scope helps doctors see the inside of the colon and watch out for suspicious areas. If anything suspicious is found, a sample of the suspicious area can be taken for a biopsy. A biopsy is a microscopic examination of the cells in a growth to determine if the cells are abnormal or cancerous. If a colon polyp, a benign growth in the colon, is found, these can also usually be removed during the colonoscopy without need for a separate surgical procedure. If the problem is known to be in the rectum or lower colon instead of further up in the large intestine, a sigmoidoscopy can be used instead of a colonoscopy. The procedure is basically the same, except the instrument is only threaded through part of the colon.
Medical imaging techniques, such as ultrasound, MRI scans, X-rays with barium dye and CT scans can also be useful for helping doctors identify and visualize growths in the colon that may be cancerous. These tests all have the same goal, but due to differences in how the procedures are done and the cost of the procedures, one may be more appropriate than the others in certain situations. Medical imaging procedures are also helpful in determining the stage of colorectal cancer, or how far the cancer has spread. The stage of the cancer has an effect on which treatments are used. A procedure called an angiography can show the blood vessels in a tumor, which can be helpful for preparation for surgery.
Blood testing may also be used during the diagnostic process for colorectal cancer. There are no specific blood tests that can definitively diagnose colorectal cancer. There are certain cancer markers that are raised in the blood in people with colorectal cancer, but a raise in the levels of these chemicals can also be caused by other conditions, such as liver or lung problems, and by smoking tobacco.