Cancer Risk: Colon growths might not be so obvious

The fight against colorectal cancer, by most accounts, is going well. With colonoscopy, doctors can prevent most of these malignancies by detecting and removing polyps, growths along the colon that can be precancerous. But some people who have had polyps removed or who have gotten a clean checkup still get diagnosed as having colorectal cancer a few years later.

A new study suggests that these out-of-the-blue cancers may arise from nonpolyp growths. Such tissues are less conspicuous than polyps, but the new data suggest that they occur with some regularity and might be more dangerous than polyps.

Researchers in Japan first noticed nonpolyp growths in colonoscopies during the 1980s and 1990s. The growths were typically flat patches of colon or rectal lining that were reddish and slightly deformed, showing patterns of disrupted blood vessels. As with polyps, some of these tissues showed abnormal growth, and Japanese doctors have since devised an easy technique for removing them during a colonoscopy.

But in the 1990s, scientists in the United States and Europe failed to find many such growths or to perceive a risk from them. Many wrote off nonpolyp growths as unique to Asians, says Roy Soetikno, a gastroenterologist at the Veterans Affairs Palo Alto Health Care System in California.

Soetikno and his colleagues performed colonoscopies in 2003 and 2004 on 1,819 veterans, predominantly white males with an average age of 64.

To discern nonpolyp growths, the U.S. physicians relied on instructions and training videos from Japanese doctors. All polyps and nonpolyp growths in the participants were removed and tested in a lab.

The physicians removed at least one colorectal polyp or nonpolyp growth from three-fifths of the veterans. Most growths were neoplastic, a grouping that includes precancerous tissues and very early cancers that haven’t moved past the lining of the colon or rectum. Overall, 10 percent of the veterans had neoplastic, nonpolyp growths, the researchers report in the March 5 Journal of the American Medical Association (JAMA).

“It is now clear that Asian and Western populations may develop [nonpolyp growths],” says physician David Lieberman of the Oregon Health & Science University in Portland, writing in the same JAMA issue.

Some patients had as many as 10 growths removed. While polyps outnumbered nonpolyp growths, lab analyses showed that the nonpolyp kind was at least five times as likely to be cancerous.

In recent years, Western scientists have debated whether colonoscopy or CT scans detect polyps better (SN: 12/6/03, p. 355; SN: 5/1/04, p. 285). “It is possible, if not likely, that additional [nonpolyp growths] may be missed by both,” Lieberman says.

“It takes some training to make [detection] automatic,” Soetikno says. Doctors are more likely to check for these growths if patients insist on it, he says. “This is contrary to the prior dogma.”

More Stories from Science News on Health & Medicine