Colon polyps 101: What are they and how are they related to colon cancer?

If you’ve read GIA’s blogs, or website material in general, you’re familiar with the emphasis that we place on the lifesaving value of screening colonoscopies to detect and remove precancerous polyps.

In order to help patients better understand what these growths are and how they relate to colon cancer, I’ll answer some basic questions about polyps.

  • What is a colon polyp?
  • Is there more than one kind of polyp?
  • Do all polyps become cancerous?
  • What are symptoms of colon polyps?
  • How are polyps removed and how does removing them prevent colon cancer? 


What is a colon polyp?
Colon polyps are growths that occur on the inner lining of the large intestine (colon) and protrude into the colon. The growths vary widely in size from a few millimeters to several centimeters. Polyps form when cells lining the colon change and become abnormal or mutate. The likelihood of a polyp becoming cancerous depends on its size, location and type. 

Is there more than one kind of polyp?All colon polyps are not the same. The cell types that make up the polyp have different characteristics that are visible when a GIA staff pathologist views them under a microscope. They also vary in size, number and location. Most importantly, polyps vary in their tendency to become malignant.

Do all polyps become cancerous?
The likelihood of a polyp becoming cancerous depends on its size, type and location in the colon. The longer a polyp is present and the greater its size, the higher the risk of it becoming malignant. In addition, people who have a genetic/family history of polyps also face a higher risk of those polyps developing into colon cancer.

Colon polyps (bottom right) can be removed completely during a screening colonoscopy, which prevents them from becoming colon cancer.

What are symptoms of colon polyps?
In the majority of cases, colon polyps themselves do not produce symptoms. Patients who have large polyps may have blood in the stool, which may or may not be visible.  Likewise colon cancer may not produce any symptoms until the disease is advanced.

How are colon polyps removed and how does removing them prevent colon cancer?
Most colon polyps are removed during a colonoscopy. During a screening test, the GI specialist searches for polyps using a flexible scope. Once found, an instrument inserted into the scope is used to remove the polyp. Removing precancerous polyps actually prevents them from becoming colon cancer.

Once removed, the polyp is sent to a pathologist to determine if it is cancerous. When polyps become extremely large or develop into colon cancer, other types of surgery may be required. GIA employs two full-time, fellowship-trained GI pathologists.

These photos were taken during free Screening Colonoscopy Day 2014 on April 5, when 41 uninsured Knoxvillians received a free colonoscopy. The large (1.5 centimeter) polyp in the photo on the left was found in the colon of a 61-year-old woman having her first screening. It would have almost certainly become cancerous within a year. The photo on the right shows the area after the polyp was completely removed.

Types of colon polyps:

Adenomatous polyp
The most common type of polyp is called an adenoma or adenomatous polyp. It is both the most common type of polyp and also the most common cause of colon cancer. The likelihood that an adenoma will become cancerous is somewhat dependent on its size; the larger the polyp, the more likely it is that the polyp will become malignant. The malignancy potential of a polyp typically rises in a polyp one centimeter in size or larger.

In addition, patients who have multiple polyps – even if they are benign – are more likely to develop additional polyps in the future that may become malignant. Having three or more polyps increases the potential for future malignancy. Finally, the shape of the cells that form a polyp is related to its potential to become cancerous. Cells that organize themselves into tubular structures are less likely to become cancerous than cells that organize themselves into finger-like structures.

Hyperplastic polyp
The second-most common type of colon polyp is the hyperplastic polyp. These polyps have little or no potential to become cancerous unless they are located in the ascending colon or are quite large in size. A person may have both hyperplastic and adenomatous polyps.

Genetic adenomatous polyp syndromes
There are several genetic conditions that run in families and are programmed into an individual’s genes. These genetic tendencies cause mutations and are passed down through the generations. In one of these conditions, hereditary polyposis, hundreds to thousands of adenomatous polyps form as a result of a gene mutation. In another, called the Lynch syndrome, polyps may become malignant and account for as many as 2 percent of all colon cancers.

It is important to recognize genetic syndromes in families because the malignant potential of these polyps is much greater than that of individuals without the genetic abnormality. For example, more than 80 percent of patients with hereditary polyposis develop colon cancer unless properly treated, even though these syndromes are responsible for only a few percent of all colon cancers. Knowing your family history of colon cancer can help uncover these genetic traits so you and your GIA physician can develop a plan for earlier and more timely screenings.