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  • Writer's pictureAlan Frischer, MD, MPH

Colon Cancer Screening

When my patients turn 50, I routinely recommend that they have a colonoscopy to screen for colorectal cancer. Not surprisingly, my generous offer is sometimes rejected. Patients express concern over drinking the prep, having general anesthesia, or undergoing the procedure itself. This fact has not escaped the medical field, and new recommendations have been issued. Various highly respected organizations, including the American Cancer Society and the US Multi-Society Task Force, currently issue guidelines on colorectal cancer screening. All recommend routine screening for colorectal cancer and polyps, usually starting at age 50 and continuing until about the age of 75.

What is colorectal cancer? It’s a disease in which abnormal cells in the colon or rectum divide uncontrollably, forming a malignant tumor. Most begin as a polyp, a growth in the tissue that lines the inner surface of the colon or rectum. Polyps are common in those over 50, and the vast majority of them are not cancerous.

However, the type of polyp known as an adenoma has a higher risk of becoming a cancer. Aside from skin cancer, which is the most common but rarely fatal form of cancer, colorectal cancer is the third most common cancer (following prostate and lung in men, and breast and lung in women).

Death rates are declining due to more screening and to a reduction in risk factors, such as a decrease in cigarette smoking. Other risk factors include a family history of colorectal cancer or a familial polyposis condition, inherited Lynch syndrome, older age, excessive alcohol use, obesity, lack of physical activity, inflammatory bowel diseases like ulcerative colitis and Crohn’s disease, and possibly diet. There are several screening tests developed to help detect colorectal cancer early, when it may be more treatable. In fact, screening can act as a form of cancer prevention as well: some tests detect precancerous polyps, which can be removed.

The standard test continues to be the colonoscopy. The rectum and entire colon are examined with a colonoscope, a flexible lighted tube with a lens for viewing and a tool for removing any abnormal growths. A thorough cleansing of the entire colon is necessary before this test, which is done by drinking large amounts of a laxative prep solution. Sedation is necessary.

An alternative visualization test is the sigmoidoscopy. This uses a shorter scope that can only view the rectum and the sigmoid colon, which is about one-third of the entire colon. It takes less time, and sedation is usually not necessary, but any cancers beyond the sigmoid colon may be missed.

There are a few other methods used for visualizing the colon, including computed tomographic (CT) colonography and double contrast barium enemas. The colonography is rarely done because it is expensive and still requires follow up with a regular colonoscopy if polyps are found. The barium enema is also seldom used, as it is less sensitive in detecting small polyps and cancers.

Other tests mainly detect cancer (but not polyps) and are less invasive, using stool samples to detect the presence of blood. Two of these tests are approved by the FDA: the FOBT (Fecal Occult Blood Test), and the FIT (Fecal Immunochemical Test). Note, however, that there are other reasons why blood might be in the stool, so this is by no means a definitive test for cancer. If positive, it still needs to be followed by colonoscopy and possibly endoscopy.

Cologuard is a new stool DNA test, approved by the FDA. It detects tiny amounts of blood in stool, similar to the FIT test, as well as nine DNA biomarkers that have been found in colorectal cancer and precancerous advanced adenomas. So, this test can detect some forms of precancerous growths. Of course, any positive test will yet again lead to a colonoscopy. An increasing number of insurance companies, including Medicare, are now covering this test.

Which test is right for you? The standard colonoscopy is still the gold standard. It allows the doctor to view the rectum and the entire colon, and a biopsy can be taken during the test. The disadvantages are that it can still miss some small polyps, flat or depressed growths, and even cancers.

The quality of the results depends on a thorough cleansing of the colon, as well as the skill and patience of the gastroenterologist. A liquid diet, prep, and sedation are necessary. Someone needs to accompany the patient to and from the procedure, and the patient may need to miss a day of work.

In June of 2017 the US Multi-Society Task Force on Colorectal Cancer issued updated screening recommendations. The most effective choices are:

• Colonoscopy every ten years, or • Annual FIT / FOBT

Less effective choices, but better than doing nothing, are:

• CT colonography every five years, or • FIT or fecal DNA every three years, or • Flexible sigmoidoscopy every five-ten years

My bottom line? It is absolutely critical that we all select a screening test, and be re-tested on a regular basis. I urge everyone between 50 and 75 to be screened for colorectal cancer, because this is a common cancer and one that can often be treated or prevented.

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