What Is an Adenoma?

Adenomas and Their Relationship to Colon Cancer

Doctor. Adam Berry / Stringer / Getty Images

An adenoma is a benign, but sometimes pre-cancerous growth that may develop in the colon. Adenomas are a type of polyp that arise from or resembles the normal lining of the colon, but have some distinctive features. Adenomas are the most common type of polyp, and also the most common cause of colon cancer, so finding and removing them through screening techniques is very important for preventing colon cancer.

 When an adenoma becomes cancerous, it is called an adenocarcinoma. Fortunately, adenomas typically are easy to find and to remove before they become cancerous.

Adenomas and Colon Cancer Screenings

Adenomas are often found during routine colon cancer screening tests, such as a colonoscopy or a flexible sigmoidoscopy. They are then sent to a pathologist who will examine them at the microscopic level and provide your physician with a sense of their composition, unique characteristics, and their risk of developing into cancer had they not been removed. 

Most adenomas develop sporadically in the population, meaning they are not caused by a genetic mutation. However, the risk of developing colon polyps larger than one centimeter or developing colon cancer is twice as great for people with a first-degree relative who has had an adenoma larger than one centimeter, so there is a well-recognized familial component.

In addition, there is a rare genetic syndrome known as familial adenomatous polyposis (FAP) that causes hundreds to thousands of adenomatous polyps to develop as a result of a gene mutation.

Adenoma Growth Patterns

Adenomas can display varying growth patterns pathologists can identify. The two major patterns are tubular and villous, and many adenomas are actually a composite of both grown patterns.

In this case, they may be referred to as tubulovillous adenomas. When adenomas are found to be noncancerous, their pathological characteristics help determine the appropriate follow-up interval and surveillance approach.

Some adenomas are described as serrated because they have a ‘saw tooth’ appearance under the microscope. Traditional serrated adenomas and sessile serrated adenomas have different features, but both are considered to be precancerous and confer an additional risk for developing colon cancer in the future. Even so, most people with serrated adenomas never develop cancer. 

Adenomas and the Likelihood of Cancer

The likelihood that an adenoma is cancerous when it is found is linked to its size, type and degree of dysplasia, or the abnormal cell proliferation. For example, a 1.5-cm tubular adenoma has a 2 percent risk of being cancerous compared with a 3-centimeter villous adenoma, which has a 25 percent risk of being cancerous. 

Colon Cancer Screening Schedules

Different doctors may recommend different intervals of time between screenings, but that interval of time will generally be shorter if a previous screening found an adenomatous polyp because your risk for developing additional adenomas is greater.

In addition, a subsequent colonoscopy may be recommended sooner or later, depending on the pathology of your previously removed adenomas: 

Years Until Next ColonoscopyPathological Characteristics of Previously Removed Adenoma
5 YearsYou had 1 or 2 tubular adenomas that were less than 1 centimeter (cm) in size
3 years

You had more than 3 tubular adenomas that were removed completely


You had 1 adenoma that was larger than 1 cm that was removed completely

Less than 3 years

You had more than 10 tubular adenomas


You had a villous adenoma


You had high-grade dysplasia

2 to 6 monthsYou had a sessile adenoma removed in pieces



Association of Directors of Anatomic and Surgical Pathology

American Cancer Society

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