A polyp is a small growth of excess tissue that often grows on the lining of the large intestine, also known as the colon. Colon and rectal polyps occur in about 25 percent of men and women ages 45 and older. Not all polyps will turn into cancer, and it may take many years for a polyp to become cancerous.
Anyone can develop colon and rectal polyps, but people with the following risk factors are more likely to do so:
- Age 45 years and older
- A family history of polyps or colon cancer
- A rare inherited gene that makes people more likely to develop polyps
- An inflammatory bowel disease, such as ulcerative colitis or Crohn’s disease
- High-fat, low-fiber diet
- Tobacco and alcohol use
- Little or no exercise
Two Types of Polyp Shapes
Polyps grow in two different shapes: flat (sessile) and with a stalk (pedunculated). Sessile polyps are more common than previously thought and harder to detect in colon cancer screening. They lie flat against the surface of the colon’s lining, also known as the mucous membrane. Pedunculated polyps are mushroom-like tissue growths that attach to surface of the colon’s mucous membrane by a long, thin stalk.
Five Types of Polyps
The large majority of polyps will not become cancers. Certain types of polyps are more likely to turn into cancer. Removal of polyps during a colonoscopy reduces the risk of developing colon cancer in the future.
The most common types of colon and rectal polyps are:
Adenomatous (tubular adenoma)
About 70 percent of all polyps are adenomatous, making it the most common type of colon polyp. When this type of polyp is found, it is tested for cancer. Only a small percentage become cancerous, but nearly all malignant polyps began as adenomatous. Fortunately, the process for these polyps to turn into colon cancer typically takes many years. With regular screening, they can be found and removed before that happens.
A type of serrated polyp, hyperplastic polyps are common, small and considered extremely low risk for turning cancerous. Typically, any hyperplastic polyps found in the colon are removed and tested to ensure they are not cancerous.
Depending on their size and location in the colon, serrated polyps may become cancerous. Small, serrated polyps in the lower colon, also known as hyperplastic polyps, are rarely malignant. Larger serrated polyps, which are typically flat (sessile), difficult to detect and located in the upper colon, are precancerous.
Inflammatory polyps most often occur in people who have inflammatory bowel disease (IBD). These types of polyps are also known as pseudopolyps because they are not true polyps, but rather develop as a reaction to chronic inflammation in the colon. Inflammatory polyps are benign and generally do not carry the risk of developing into colon cancer.
Villous Adenoma (Tubulovillous Adenoma)
Approximately 15 percent of polyps detected in colon cancer screening are villous or tubulovillous adenomas. This type of polyp carries a high risk of turning cancerous. They are commonly sessile, which makes them more difficult to remove. Smaller villous adenoma polyps may be removed during a colonoscopy, while larger polyps of this type may require surgery for complete removal.
Polyps can be detected and safely removed during a colonoscopy, preventing them from turning into cancer. Large polyps may require more than one treatment, and in some patients surgery could be required for complete removal. If you have an increased risk for colon polyps, talk with your doctor about the types and frequency of tests that will be best for you.
What are Complex Polyps?
Complex polyps (sometimes referred to as “defiant polyps” in the medical literature) are those polyps that possess one of the following features: size greater than 2 centimeters, in a location unfavorable or too sessile for removal by more straightforward techniques, or simply polyps that the doctor performing your colonoscopy does not feel they can safely remove.