Traditional serrated adenoma (TSA)

by Jason Wasserman MD PhD FRCP
July 19, 2025

A traditional serrated adenoma is a type of polyp that develops on the inner lining of the colon or rectum. Although these polyps are not cancer, they are considered precancerous, which means they can turn into cancer over time if not removed. Most traditional serrated adenomas are found during a routine colonoscopy and are removed at that time.

Traditional serrated adenomas are less common than other types of polyps such as tubular adenomas or hyperplastic polyps. Most are found in the rectum and the lower (distal) part of the colon, although some may arise in the upper (proximal) colon. They are usually found during routine colonoscopy screenings.

Is a traditional serrated adenoma a type of cancer?

No, a traditional serrated adenoma is not cancer. However, it is considered a precancerous polyp because over time it can develop into colorectal cancer. For this reason, doctors usually recommend that traditional serrated adenomas be completely removed and that follow-up colonoscopies be performed to monitor for new polyps.

What causes a traditional serrated adenoma?

The exact cause is not fully understood, but research suggests that traditional serrated adenomas develop as part of a pathway called the serrated pathway. This pathway involves a series of genetic and epigenetic changes, including mutations in genes such as BRAF or KRAS. These changes lead to abnormal growth and transformation of the cells lining the colon.

Traditional serrated adenomas may arise on their own or in association with other types of serrated polyps such as hyperplastic polyps or sessile serrated lesions. In many cases, they form through a step-by-step process that starts with a small polyp and progresses to larger, more abnormal growths over time.

How is the diagnosis made?

The diagnosis is made after a pathologist examines a tissue sample under the microscope. The sample is usually obtained during a colonoscopy, a procedure where a doctor uses a thin, flexible tube with a camera to look at the inside of your colon and remove any polyps that are found.

The pathologist looks for specific features that define a traditional serrated adenoma, such as a serrated (sawtooth) pattern, tall cells with pink (eosinophilic) cytoplasm, and slit-like spaces between the cells. These features distinguish traditional serrated adenomas from other types of polyps.

What does a traditional serrated adenoma look like under the microscope?

Under the microscope, traditional serrated adenomas have a unique appearance. The lining of the polyp shows long, finger-like projections with narrow, slit-shaped spaces between the cells. The cells are tall and column-shaped, with bright pink cytoplasm and pencil-shaped (elongated) nuclei.

Some traditional serrated adenomas also contain ectopic crypts. These are abnormal gland structures that do not connect to the underlying tissue and often appear on the sides of the finger-like projections. These features help the pathologist confirm the diagnosis.

What does dysplasia mean?

Dysplasia is an abnormal pattern of cell growth that can lead to cancer over time. Pathologists look for dysplasia when examining polyps like traditional serrated adenomas under the microscope. Dysplasia means the cells are not growing, maturing, or behaving normally. These changes do not mean cancer is present, but they indicate a higher risk of cancer developing in the future.

In traditional serrated adenomas, dysplasia can vary in severity. Most pathologists categorize dysplasia in a traditional serrated adenoma as either low grade or high grade based on the changes seen under the microscope.

Traditional serrated adenoma with low grade dysplasia

Most traditional serrated adenomas show low grade dysplasia. This means the cells look abnormal but the changes are mild. These polyps are still considered precancerous and are removed to prevent progression to cancer.

Traditional serrated adenoma with high grade dysplasia

In some cases, the dysplasia is more severe, and the polyp is classified as having high grade dysplasia. This means the abnormal cells are more advanced and the risk of developing colorectal cancer is higher. If high grade dysplasia is seen, your doctor may recommend closer follow-up.

Can a traditional serrated adenoma come back after it is removed?

If a traditional serrated adenoma is completely removed during colonoscopy, it usually does not grow back in the same spot. However, people who have had a traditional serrated adenoma are at higher risk of developing new polyps in the future. For this reason, doctors typically recommend repeat colonoscopies to monitor for new growths and catch any new polyps early.

What is the risk of developing cancer?

Traditional serrated adenomas are considered high-risk polyps because they have the potential to develop into colorectal cancer if left untreated. The risk is higher if the polyp is large (greater than 1 cm), located in the upper colon, or shows high grade dysplasia. Removing the polyp eliminates this risk at that site, but ongoing surveillance is important.

Questions to ask your doctor

• Was the entire traditional serrated adenoma removed?

• Did the pathology report show low grade or high grade dysplasia?

• Were the margins of the polyp clear of abnormal cells?

• How often should I have follow-up colonoscopies?