When examining stool, doctors look for microscopic amounts of blood, which are shed from colon tumors. There is a concern that stool testing may become less effective over time compared to screening, as only larger tumors shed blood, and if the tumor is removed it may make stool testing less effective.
In order to achieve their findings, researchers tracked annual fecal blood tests performed on nearly 325,000 patients over the course of four years.
In the first year of testing, stool testing diagnosed colon cancer in 84.5 percent of patients. “We found that the sensitivity for cancer was somewhat higher in the first year, and that’s not surprising. The first year you screen someone, for breast cancer or for anything, you’re going to find cancers that have been there for a while that may be larger or are easier to detect,” said co-author Dr. Douglas Corley.
After two to four years effectiveness of stool testing varied between 73 and 78 percent, which means it is still effective in picking up new tumors.
“We really can find early cancers continuously as they’re getting bigger. And over a 10-year period this test is in all likelihood going to prevent the same number of deaths as a colonoscopy performed once every 10 years,” added Dr. Richard Wender, chief cancer control officer at the American Cancer Society.
Although stool testing is effective for diagnosing colon cancer, colonoscopy still has advantages, as it has close to 100 percent effectiveness in diagnosis and is conducted once every 10 years. Wender added, “You find early cancers, you remove all the polyps, and it buys you 10 years of protection.”
Unfortunately, colonoscopy is quite an invasive procedure with some uncomfortable preparation, and so if it is the only option, many individuals may choose not to undergo colon screening. Stool testing then allows for more individuals to get screened, as there is another option available aside from colonoscopy.