How Colon Polyp Size, Shape and Growth Pattern Affect Cancer Risk

You’ve had a colonoscopy and now you start reading the report and grow a little worried seeing the word “polyps” in the text. Does that mean you definitely have colorectal cancer?

For starters, no. The vast majority of colorectal polyps are harmless growths that sprout on the lining of your colon or rectum. They’re pretty common, especially in adults age 45 or older.

But that doesn’t mean polyps should be ignored, says colorectal surgeon Rebecca Gunter, MD. Colorectal cancer begins in polyps, after all. Finding and removing those polyps decreases your risk of developing the disease.

So, what’s the difference among polyps, and are some more worrisome than others? Dr. Gunter explains.

Colon polyp size

The smaller the polyp, the less likely it is to be on the road to cancer, says Dr. Gunter. Polyps can range in size from the less-than-5-millimeter “diminutive” category to the over-30-millimeter “giants.”

Why the size matters

To put those sizes in perspective, a diminutive polyp is about the size of a match head. Larger polyps can be almost as big as the average person’s thumb.

Studies show that few smaller polyps are cancerous. As polyps slowly grow, however, the cancer risk rises. It’s estimated that it takes about 10 years for cancer to form into a colorectal polyp.

Colon polyp shape

Polyps come in three basic shapes, says Dr. Gunter. They are:

  • Sessile polyps are dome-shaped and grow flat on your colon wall. About 85% of polyps are in this group. Sessile polyps can be snared and removed somewhat easily in a colonoscopy, though larger ones are typically taken out in pieces.
  • Pedunculated polyps hang from a stalk attached to your colon wall. (Think of a cherry on a stem.) They’re easy to spot and can usually be removed in one piece during a colonoscopy. Cancer can develop on the head of pedunculated polyps.
  • Flat polyps are the least common polyps, making up about 2% of discovered lesions. They’re the most challenging to remove and sometimes difficult to locate.

Colon polyp growth patterns

Doctors examine removed polyps under a microscope for a close-up look at their cells. The review is to determine levels of dysplasia, a term used to describe how cancerous polyps appear on a cellular level.

Polyps with signs of high-grade dysplasia have disorganized cells with a larger, darker center. These dysplastic cells often grow wildly, a sign that cancer may have been close to forming in the polyp.

Your healthcare provider may recommend a follow-up colonoscopy sooner than normal if they find polyps with high-grade dysplasia. “It’s a finding that warrants increased attention,” notes Dr. Gunter.

Polyps with cells that look only mildly abnormal are labeled as having low-grade dysplasia and are of less concern.

What is an adenoma?

Adenomas are polyps made from tissue that looks like the usual lining of your colon but isn’t. There are three kinds of adenomas, which doctors can determine by looking under a microscope. The types are:

  • Tubular. These adenomas look like tiny tubes jammed into your colon lining. They’re typically smaller in size and less worrisome.
  • Villous. This type of adenoma sprawls out like the fronds of a fern, a sign of faster and more chaotic growth. Villous adenomas are usually larger and more likely to be cancerous.
  • Tubulovillous. This type is a mixture of tubular and villous adenomas, with characteristics of each.

How are serrated polyps different?

Serrated polyps look like saw teeth under the microscope. They’re subtle, pale and without much form, making them easier to overlook during a colonoscopy. About 25% of colon cancers come from serrated polyps.

Should polyps be removed?

The answer is simple: Yes.

Though not all polyps turn into cancer, all colorectal cancers start as polyps. Removal eliminates the threat posed by a polyp. Keeping up with your colonoscopies allows your doctors to do just that.

Colonoscopies are recommended for everyone starting at age 45, or earlier if you have higher risk factors such as a family history of colon cancer. (Stool tests also are an option to screen for colon cancer, but colonoscopies remain the recommended method.)

“The reality is that colon polyps are fairly common,” says Dr. Gunter. “The good news is that removing them decreases your risk of colorectal cancer. A colonoscopy is a safe and effective procedure that could be life-saving. Don’t delay getting it done.”

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