Sessile serrated adenoma of the large intestine

By Jason Wasserman MD PhD FRCPC
May 20, 2025

A sessile serrated adenoma (SSA) is a non-cancerous growth found in the colon. Although SSAs themselves are not cancer, they are considered precancerous, meaning they can potentially turn into a type of colon cancer called adenocarcinoma over time. Due to this risk, doctors usually recommend completely removing SSAs to prevent them from developing into cancer.

Another name for sessile serrated adenoma is sessile serrated lesion (SSL). Both terms describe the same condition.

Where are sessile serrated adenomas usually found?

SSAs commonly occur on the right side of the colon, especially in regions known as the cecum, ascending colon, and transverse colon. However, they can appear anywhere in the colon or rectum.

Does a sessile serrated adenoma mean cancer?

No, having an SSA does not mean you have cancer. However, because SSAs are precancerous, they have the potential to develop into a type of colon cancer called adenocarcinoma if left untreated. Complete removal of an SSA significantly lowers the risk of it progressing into cancer.

What is the difference between a sessile serrated adenoma and a polyp?

In pathology, a polyp is a general term used to describe any growth extending from the surface of tissue. Because of the way it grows, an SSA is one specific type of polyp. However, not all polyps are SSAs. Other types of colon and rectal polyps include:

• Tubular adenomas: Polyps that may develop into cancer over time.

• Tubulovillous adenomas: Polyps with features of both tubular and villous adenomas.

• Villous adenomas: Polyps with a higher risk of becoming cancerous.

• Hyperplastic polyps: Generally considered non-precancerous polyps.

• Traditional serrated adenomas: Precancerous polyps similar to SSAs but with distinct microscopic features.

How is the diagnosis of sessile serrated adenoma made?

Doctors typically diagnose an SSA after it is removed during a colonoscopy. The adenoma may be removed in one piece or in multiple smaller fragments. A pathologist then examines the tissue under a microscope.

SSAs can be challenging for doctors to detect during colonoscopies because they often appear flat, subtle, and blend with the surrounding colon lining.

What is a sessile serrated adenoma with dysplasia, and why is dysplasia important?

Dysplasia is an area of abnormal cell growth that can eventually lead to cancer. Colon cancer developing from an SSA usually starts from areas of dysplasia. Because dysplasia significantly increases the risk of developing cancer, pathologists carefully examine SSAs for signs of dysplasia.

Historically, dysplasia was classified as low or high grade, but this is no longer recommended. Today, any dysplasia detected within an SSA is considered important and may lead to a recommendation for closer follow-up.

Although complete removal of all SSAs is important, finding dysplasia may prompt your doctor to recommend a follow-up colonoscopy sooner, especially if the SSA wasn’t fully removed during the first procedure.

What is a margin?

The margin refers to the edge or boundary where the adenoma (polyp) was removed from the colon or rectum. Pathologists usually do not specify whether the SSA was completely removed, as the doctor performing the colonoscopy can better judge completeness.

Because SSAs are often removed in multiple fragments, it might be difficult or impossible for the pathologist to clearly identify the true margin. In these situations, the margin might not be specifically mentioned in your pathology report.

However, if cancer is found within an SSA, your pathology report should clearly state how close the cancer is to the margin, as this can affect future treatment decisions.

What is the risk of developing cancer with a sessile serrated adenoma?

Most SSAs will never become cancerous. However, they do have a higher risk of developing into colon cancer compared to some other polyp types (for example, hyperplastic polyps). The exact risk depends on various factors, such as the adenoma’s size, how long it has been present, and whether dysplasia has formed. In general, larger SSAs (greater than one centimeter) or those with dysplasia carry a higher risk. Doctors typically recommend complete removal and regular follow-up colonoscopies to manage this risk effectively.

Can a sessile serrated adenoma grow back after being removed?

If an SSA is entirely removed during colonoscopy, it usually does not grow back. However, if the SSA was only partially removed and small portions remain, there is a chance it could regrow. Because SSAs can sometimes be difficult to see and remove completely, regular follow-up colonoscopies are recommended after removal to confirm that no new adenomas have appeared and the original lesion has not returned.

Questions to ask your doctor

If your pathology report mentions a sessile serrated adenoma (SSA), you might want to ask your doctor:

• Was my SSA completely removed during the colonoscopy?

• Did the SSA show any dysplasia?

• When should I schedule my next colonoscopy?

• How can I lower my risk of developing colon cancer in the future?

Understanding the term sessile serrated adenoma helps you actively participate in your healthcare and have informed conversations with your medical team.