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, a new study finds.
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 was not involved in the study. “You’re not going to be able to do seven-minute colonoscopies.”
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.
Doctors have known about flat growths but haven’t recognized their danger, experts said.
While knobby polyps were found in four times as many participants, more than half 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 as likely to be cancerous as the polyps. They believe the growths represent a separate colon cancer pathway, rather than being precursors to knobby polyps, Soetikno said. The study appears in today’s Journal of the American Medical Association.
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. “It will heighten people’s awareness that, yes, these are found in United States.”
The findings came from colonoscopies of more than 1,800 mostly male military veterans who were seen at one Department of Veterans Affairs center from July 2003 to June 2004. Doctors involved had been trained by Japanese specialists to use a dye during colon oscopies to spot flat growths.
Colorectal cancer is the nation’s second-leading cancer killer.
