In many cases, colon or rectal cancer is found after symptoms appear. This is why getting tested regularly for colorectal cancer is so important. Regular testing, also called screening, can be helpful in detecting any abnormal areas, such as a polyps, before they become cancer, or if they are cancerous, much earlier which makes it easier to treat.
The American Cancer Society recommends regular colon screening for most people starting at age 50. But talk with your doctor about the right timing for you, especially if you have family members that have been diagnosed with colon or rectal cancer.
Colorectal Cancer Early Detection and Diagnosis Methods
Doctors use a variety of tests that examine the colon and rectum to detect (find) and diagnose colon cancers. The following tests and procedures may be used, even if symptoms aren’t present:
- Physical exam and history: An exam of the body to check general signs of health, including checking for signs of disease, such as lumps or anything else that seems unusual. A history of the patient’s health habits and past illnesses and treatments will also be taken.
- Digital rectal exam: An exam of the rectum. The doctor or nurse inserts a lubricated, gloved finger into the rectum to feel for lumps or anything else that seems unusual.
- Standard (or optical) colonoscopy. In this test, the rectum and entire colon are examined using a colonoscope, a flexible lighted tube with a lens for viewing and a tool for removing tissue. Like the shorter sigmoidoscope, the colonoscope is inserted through the anus into the rectum and the colon as air (or carbon dioxide) is pumped into the colon to expand it so the doctor can see the colon lining more clearly. During colonoscopy, any abnormal growths in the colon and the rectum can be removed, including growths in the upper parts of the colon that are not reached by sigmoidoscopy. A thorough cleansing of the entire colon is necessary before this test. Most patients receive some form of sedation during the test. The colonoscopy is the most common test used for detecting and diagnosing colon and rectal cancer.
- Virtual colonoscopy. This screening method, also called computed tomographic (CT) colonography, uses special x-ray equipment (a CT scanner) to produce a series of pictures of the colon and the rectum from outside the body. A computer then assembles these pictures into detailed images that can show polyps and other abnormalities. Virtual colonoscopy is less invasive than standard colonoscopy and does not require sedation.
- Biopsy: The removal of cells or tissues so they can be viewed under a microscope by a pathologist to check for signs of cancer.
- High-sensitivity fecal occult blood tests (FOBT). Both polyps and colorectal cancers can bleed, and FOBT checks for tiny amounts of blood in feces (stool) that cannot be seen visually. (Blood in stool may also indicate the presence of conditions that are not cancer, such as hemorrhoids.) There are currently two types of FOBT that have been approved by the Food and Drug Administration (FDA). The first, guaiac FOBT (gFOBT), uses a chemical to detect heme, a component of the blood protein hemoglobin. The second, fecal immunochemical (or immunohistochemical) test (FIT, also known as iFOBT), uses antibodies to detect human hemoglobin protein specifically. For each type of FOBT, patients will collect a stool sample using a kit and return it to the doctor for testing.
- Barium enema: A series of x-rays of the lower gastrointestinal tract. A liquid that contains barium (a silver-white metallic compound) is put into the rectum. The barium coats the lower gastrointestinal tract and x-rays are taken. This procedure is also called a lower GI series.
- Stool DNA test (FIT-DNA). The only stool DNA test approved by the FDA to date, Cologuard®, is a multitarget test that detects tiny amounts of blood in stool (with an immunochemical test similar to FIT) as well as nine DNA biomarkers in three genes that have been found in colorectal cancer and precancerous advanced adenomas. The DNA comes from cells in the lining of the colon and rectum that are shed and collect in stool as it passes through the large intestine and rectum. Patients will collect a stool sample using a kit that will be mailed to a laboratory for testing.
- Sigmoidoscopy. In this test, the rectum and sigmoid colon are examined using a sigmoidoscope, a flexible lighted tube with a lens for viewing and a tool for removing tissue. This instrument is inserted through the anus into the rectum and sigmoid colon as air (or carbon dioxide) is pumped into the colon to expand it so the doctor can see the colon lining more clearly. During sigmoidoscopy, abnormal growths in the rectum and sigmoid colon can be removed for analysis (biopsied). The lower colon must be cleared of stool before sigmoidoscopy, but the preparation is less extensive than that required for colonoscopy. People are usually not sedated for this test.