CHICAGO— Flat growths on the colon wall are more common in Americans than previously thought and more likely to be cancerous than the more familiar knobby masses known as polyps, according to a study appearing in today's Journal of the American Medical Association.
New techniques can locate and remove the flat growths, but many doctors aren't aware of their cancer risk and may not know how to look for them. The findings are likely to change the practice of colonoscopy, experts said, and may explain some colon cancers that arise between colonoscopies.
"I think it is very important. It's going to intensify the need for quality screening," said Dr. Stephen Hanauer, gastroenterology chief at the University of Chicago, who wasn't involved in the study.
The growths tend to be smaller when they are cancerous — the size of a nickel instead of a quarter — and are level with the colon wall or depressed like a pothole. They blend in with the surrounding tissue and are difficult to spot.
"They look like a pancake just lying on the floor," said the study's lead author, Dr. Roy Soetikno of the Veterans Affairs Palo Alto Health Care System in California. The Palo Alto Institute for Research and Education, a nonprofit group associated with that VA system, funded the study.
Doctors have known about flat growths but haven't recognized their danger, experts said.
While knobby polyps were found in four times as many study participants, more than half of the colon cancers found — 15 of 28 — were in flat and depressed growths. Thirteen were in polyps.
Researchers found the flat growths were nearly 10 times more likely to be cancerous than the polyps. They believe the growths represent a separate colon cancer pathway, rather than being precursors to knobby polyps, Soetikno said.
Since the 1980s, Japanese doctors have reported more flat colon growths than were seen in the United States, but Western scientists doubted their importance, said Dr. David Lieberman of the Oregon Health and Science University in Portland, who wrote an editorial in the journal.
"This paper will have a big impact on gastroenterology," Lieberman said.
The findings came from colonoscopies of more than 1,800 mostly male veterans who were seen at one VA center from July 2003 to June 2004. Flat and depressed growths were detected in 170 patients, nearly 10 percent. Knobby polyps were found in 675 patients, about 37 percent.