The gold standard test for detecting it: colonoscopies. But now a new study suggests doctors may have been missing a key indicator for colorectal cancer in Americans.
"The teaching has always been that most colon cancer starts as a polyp, a plum-like growth on the lining," said Dr. Isaac Bartley.
Gastroenterologist Dr Isaac Bartley says for years doctors were tuned into finding polyps -- knobby masses in the colon. Now it turns out "flat growths" in the colon may actually be more dangerous.
"Even though we knew that sometimes there may be flat growth, we didn't realize that they would be this common. We know our Japanese colleagues have talked about these flat growths," said Dr. Bartley. "We have not really been seeing them in the United States. Now whether or not it's because we're not looking for them, or they're not that common, that's the issue at hand."
In a one-year study of 1,800 veterans at a VA center, doctors found that while knobby polyps were identified in four times as many participants, more than half of the colon cancers detected came from the group with flat growths.
And researchers say the flat growths were nearly 10 times more likely to be cancerous than the polyps.
Researchers say the most cancerous of the flat growths appear to be smaller, about the size of a nickel. They're level with the colon wall, or depressed like a pothole. They blend in with surrounding tissue and more importantly they are difficult to spot.
Which is why these findings may well change the way doctors manage their patients' colonoscopies.
"We're going to take time looking and we're going to look carefully, and we're going to make sure we don't miss any of these flat lesions," said Dr Bartley.
Dr. Bartley says patients will have to be vigilant as well, and find a doctor that will take their time reviewing the screening. Because colorectal cancer is slow-growing, colonoscopies are recommended every 10 years, starting at the age of 50. Experts say this study may explain why some colon cancers show up between screenings. They add that the findings underline the importance of getting a high-quality colonoscopy every time.