Colon Polyps: Which Ones Are Riskiest for You?

You’ve had your colonoscopy and received a pretty confusing report.

What do all those long words mean? And which polyps are most likely to lead to colorectal cancer?

“We often can’t tell which polyps are bad by looking at them. We have to remove them, then study samples under a microscope,” says colorectal surgeon James Church, MD.

Here, he explains how polyps vary by shape, size and growth pattern.

What a polyp’s shape suggests

Polyps — lumps on the smooth lining of the colon or rectum — are increasingly common after age 40. Doctors find and remove polyps during colonoscopy.

• About 85 percent of polyps are “sessile”: dome-shaped, without a stalk.
• About 13 percent of polyps are “pedunculated,” hanging from the colon wall on a stalk like a cherry on a stem.
• About 2 percent of precancerous lesions are flat.

Although sessile polyps can be snared easily, very large sessile polyps must be removed in pieces.

Pedunculated polyps are easier to spot and can be removed in one piece. “The head is where the precancer would be, so by snaring the stalk, we know without a doubt that it’s gone,” he says.

Flat polyps are the most challenging to take off. “They can be quite subtle and easy to miss,” says Dr. Church.

Why a polyp’s size matters

The smaller the polyp, the less likely it is to be on the road to cancer, he notes.

Polyps range from the less-than-5-millimeter “diminutive” size to the over-30-millimeter “giant” size.

“A diminutive polyp is only about the size of a match head,” he says. “A large polyp can be almost as big as the average person’s thumb.”

Polyps larger than 20 millimeters have a 10 percent chance of already having cancer in them.

Understanding dysplasia

The first thing doctors examine under the microscope is what polyp cells look like. “Precancerous cells look wild,” says Dr. Church. “This wildness is called dysplasia.”

Dysplastic cells can no longer control their own growth. They look more disorganized and have larger, darker centers than normal cells.

Cells with low-grade dysplasia aren’t too different from normal cells. “But cells with high-grade dysplasia look really wild, like cancer cells,” he says.

“When a polyp shows high-grade dysplasia, we’re happy to get it out, because cancer is not far away.”

Adenomas vs. serrated polyps

Seventy-five percent of colon cancers come from polyps called adenomas, arising from glandular cells in the colon lining.

“Adenomas are often pinker, distinct and on stalks, and are quite easy to remove,” says Dr. Church.

Twenty-five percent of colon cancers come from serrated polyps, which look like saw teeth under the microscope.

“Serrated polyps are subtle, pale and without much form. They are easy to miss during colonoscopy.”

Villous vs. tubular adenomas

A series of “crypts,” resembling tiny wells covered with cells, form the colon lining. A polyp’s crypts can look “tubular” or “villous” under the microscope:

• In tubular adenomas, crypts are aligned normally and look like tiny test tubes jammed into the colon lining.
• In villous adenomas, crypts are disordered and resemble the fronds of a fern, indicating faster growth.

Villous changes are more worrisome. “The bigger the polyp, the more likely we are to see high-grade dysplasia and villous changes,” notes Dr. Church.

“Though not all polyps turn into cancer, all cancers start as polyps. That means we must remove them all.”

Keeping up with your colonoscopies will allow your doctors to do just that.