Tubular adenoma of the colon and rectum

A tubular adenoma is a type of colorectal polyp that forms on the inner lining of the large intestine, which includes the colon and rectum. It is considered a conventional adenoma, which means it develops through the most common pathway that can lead to colorectal cancer.

Although tubular adenomas are benign (non-cancerous), they are classified as precancerous because they have the potential to develop into a type of cancer called adenocarcinoma over time if left untreated. For this reason, tubular adenomas are removed when found and monitored through follow-up colonoscopy.

Where are tubular adenomas found?

Tubular adenomas can develop anywhere in the large intestine, from the beginning of the colon (near the small intestine) to the end of the rectum. They may be found during routine colonoscopies, which are done to screen for colorectal cancer, or when investigating symptoms such as bleeding or changes in bowel habits.

Is a tubular adenoma a type of cancer?

No. A tubular adenoma is not cancer, but it is considered precancerous. This means that if it is not removed, it may slowly develop into cancer over time. The risk of this happening depends on several factors, including the size of the polyp and the degree of cellular changes (called dysplasia) seen under the microscope.

What causes a tubular adenoma?

Tubular adenomas develop through mutations (changes) in the DNA of colon cells. These mutations are usually acquired over time and are not inherited. However, some people have an increased risk due to:

• Age (most common after age 50).

• Family history of colon polyps or colorectal cancer.

• Inherited conditions, such as familial adenomatous polyposis (FAP) or Lynch syndrome.

• Lifestyle factors, including low-fiber, high-fat diets, smoking, obesity, lack of physical activity.

What are the symptoms of a tubular adenoma?

Most tubular adenomas do not cause symptoms and are found by chance during routine screening. However, larger polyps may cause:

• Blood in the stool or rectal bleeding.

• Changes in bowel habits, such as constipation or diarrhea.

• Abdominal pain or discomfort.

Occult bleeding (bleeding that is not visible to the eye) can be detected using stool-based screening tests.

How is a tubular adenoma diagnosed?

Tubular adenomas are diagnosed after the polyp is removed during colonoscopy. A pathologist examines the polyp under a microscope and looks for:

• The type of polyp (tubular, tubulovillous, or villous).

• The degree of dysplasia (low grade or high grade).

• The size and whether the polyp was completely removed.

• Any signs of invasion, which would suggest cancer.

What does a tubular adenoma look like under the microscope?

Under the microscope, a tubular adenoma is made up of tube-like glands formed by dysplastic (abnormal) cells. The architecture of the colon lining is altered, and the cells may appear elongated, darker-staining, and stratified (stacked). These changes are signs of dysplasia, a form of abnormal cell growth that is not yet cancer but may lead to cancer if left untreated.

Tubular adenomas can have different shapes:

• Pedunculated polyps grow on a stalk.

• Sessile polyps are flat or slightly raised.

• Flat or depressed polyps are harder to detect but still carry a risk.

A small amount of villous (finger-like) growth is common in tubular adenomas. If the polyp has more than 25% villous features, it may be classified as a tubulovillous adenoma or a villous adenoma, which are considered higher-risk types.

Low grade versus high grade dysplasia in a tubular adenoma

All tubular adenomas show dysplasia, which is a term pathologists use to describe cells that are growing abnormally but are not yet cancer. Dysplasia is important because it helps determine how likely the adenoma is to progress into cancer if left untreated. Pathologists divide dysplasia into two levels: low grade and high grade.

Tubular adenoma with low grade dysplasia

This is the most common type of tubular adenoma. In a tubular adenoma with low grade dysplasia, the cells look mildly abnormal under the microscope. They may have darker and more crowded nuclei than normal colon cells, but they are still relatively organized, and the overall structure of the polyp remains orderly.

The risk of cancer in a tubular adenoma with low grade dysplasia is very low, especially if the polyp is small. However, these polyps are still considered precancerous, and doctors typically recommend removing them to prevent future problems.

Tubular adenoma with high grade dysplasia

In a tubular adenoma with high grade dysplasia, the cells are very abnormal. These cells often show signs of faster growth and less organization under the microscope. Features may include large, irregularly shaped nuclei, prominent nucleoli, and loss of normal tissue structure.

Although this is not cancer, a tubular adenoma with high grade dysplasia is closer to becoming cancer than one with low grade dysplasia. If not removed, there is a higher chance it could eventually develop into colorectal cancer. For this reason, tubular adenomas with high grade dysplasia should be completely removed, and follow-up may be recommended sooner to check for new or recurring polyps.

What is an advanced adenoma?

An advanced adenoma refers to a polyp with one or more of the following features:

• Larger than 10 mm.

• High grade dysplasia.

• Villous or tubulovillous architecture.

Advanced adenomas have a higher chance of developing into cancer and are more likely to be associated with other polyps. People with advanced adenomas typically need more frequent colonoscopies to monitor for recurrence or new polyps.

What is a margin?

The margin is the edge of the tissue removed during colonoscopy. If a polyp is removed in one piece, the pathologist can usually determine whether it was completely removed:

• A negative margin means no abnormal cells were found at the edge, suggesting complete removal.

• A positive margin means abnormal cells were found at the edge, which may mean some polyp tissue was left behind.

Polyps removed in small fragments may not have a clear margin, and this will be noted in the pathology report.

Can a tubular adenoma come back after removal?

If a tubular adenoma is completely removed, it usually does not return. However, people who develop one adenoma are at higher risk of developing new polyps in the future. This is why your doctor will recommend regular follow-up colonoscopies after polyp removal.

Questions to ask your doctor

• Did my tubular adenoma have low grade or high grade dysplasia?

• Was it completely removed?

• Do I need to have another colonoscopy soon?

• What can I do to lower my risk of more polyps?