A new look at colon cancer screening

A new look at colon cancer screening – Harvard Health – November 2016

Don’t be intimidated about screening tests. The latest guidelines suggest you can choose from multiple strategies.

Colon cancer continues to be the country’s second leading cause of cancer-related deaths and the third most common cancer in men, according to the CDC. It almost always develops from precancerous polyps (abnormal growths).

Screening tests, which are recommended for men ages 50 to 75, help find and sometimes aid removal of polyps before they become cancer. 

“The reality is that when it comes to colon cancer screening, men only think of a colonoscopy, which is invasive and requires a bowel preparation and intravenous sedation,” says Dr. Leigh Simmons, medical director of the Health Decision Sciences Center at Harvard-affiliated Massachusetts General Hospital.

“But there are other tests that might be a better option, especially for lower-risk men.” [and women] 

The need to be proactive

To help highlight the urgency for regular colon cancer screenings, the U.S. Preventive Services Task Force (USPSTF) recently issued updated guidelines that identified seven approved methods and their efficicacy based on the most recent clinical trials.

They were divided into two groups:

  1. stool-based tests and
  2. direct visualization tests.

While the USPSTF did not endorse any specific test, its report does stress the urgency of testing.

“The best screening test for colon cancer is the one that gets done,”
says Dr. Simmons

Stool-based tests

These noninvasive tests are inexpensive and easy to perform.

If the results show possible signs of colon cancer, you may then need a visualization test. If results are normal, you can be retested every one to three years.

Guaiac-based fecal occult blood test ( gFOBT ).

Your doctor gives you the test kit, which you use at home, without any need for bowel preparation.

You place a stool sample on a test card coated with a substance called guaiac, which changes color if blood is in the stool (a possible sign of polyps or cancer).

You collect three samples in a row, place them in a supplied container, and return them to your doctor’s office for analysis.

Effectiveness: According to the USPSTF report, when the patient has colon cancer, the test is likely to indicate its presence 62% to 79% of the time.

Fecal immunochemical test (FIT).

As with the gFOBT, you perform at home with no bowel prep. Also, there are no diet or drug restrictions. It tests for hidden blood by reacting to part of the human hemoglobin protein, which is found in red blood cells.

Effectiveness: The FIT can be more accurate than a gFOBT because it is less likely to react to bleeding from other parts of the digestive tract, like the stomach or a hemorrhoid.

Multitargeted stool DNA test.

This test combines FIT with testing for altered DNA biomarkers in cells shed into the stool. It is given every three years.

Effectiveness: Statistically, the stool DNA test results in more false positives than a FIT (that is, it is more likely to signal a problem when there is none) and thus is more likely to lead to unnecessary colonoscopies. However, it also detects more polyps and cancers than FIT alone.

Direct visualization tests

If you show signs of possible colon cancer, your doctor may want to perform one or more of the following tests to better diagnose your condition.

Colonoscopy.

The most familiar colon screening, it requires at least one day of full bowel prep to clean the colon of stool, and many patients have sedation during the procedure.

Effectiveness: The procedure offers the most comprehensive look at the entire colon. If the doctor sees polyps during the test, he or she can biopsy or remove them on the spot.

CT colonography .

Similar prep is required as with a colonoscopy, but no sedation is needed. The doctor often can view the entire colon, but cannot remove polyps (that takes a colonoscopy).

Effectiveness: Studies are limited, but there is a risk for false-positive results. Some studies suggest it can cause more discomfort than a colonoscopy.

Flexible sigmoidoscopy.

Similar to a colonoscopy, except the video camera is attached to a shorter and thinner tube (about two feet long and about as thick as your little finger). As with a colonoscopy, the rectum and lower colon must be clean of stool.

Effectiveness: Studies suggest the screening is less beneficial than a colonoscopy since it examines about one-third of the colon. Also, the doctor can remove polyps only from the examined area.

Flexible sigmoidoscopy with FIT.

This combination test is an option for people who want an endoscopic screening and possibly lower the need for a colonoscopy.

Effectiveness: Initial findings suggest it offers a balance between benefits and potential harms like false positives.  

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