What Is Tubular Adenoma?

Overview

A tubular adenoma is an abnormal growth of glandular tissue that grows on the walls of the colon or rectum. Tubular adenomas are the most frequently occurring type of colon polyps, accounting for over 80% of all diagnosed cases. Since tubular adenomas have the potential of progressing into colorectal cancer, it is crucial to remove them as soon as they are detected. 

Colonic adenomas

The large intestine is an organ that measures approximately 1.5 metres. It is a hollow muscular tube made up of the colon and rectum that connects the small intestine to the anus. One of the main functions of the large intestine is to absorb the remaining water, nutrients, and vitamins from the waste left over from the small intestine. This results in a dehydrated and compact waste, known as stool, which is moved towards the rectum for elimination. 

A polyp is an umbrella term for abnormal tissue growth. Polyps can grow in various parts of the body, although typically, they grow in mucous membranes like the colon, nose, or cervix. Colorectal polyps can be divided into several subtypes, including hyperplastic polyps, inflammatory polyps, and adenomas.  

An adenoma is a polyp that forms in glandular tissue, meaning there is an abnormal growth of glandular cells.¹ Colonic adenomas grow in the colon and rectum and are the most common type of polyp in the colon. In fact, 20% to 53% of the population in the United States older than 50 years old is estimated to have colonic adenomas.² 

Adenoma classification

Adenomas can be classified into sessile, pedunculated, or sub pedunculated, depending on the shape of the polyp and how it attaches to the walls of the colon. Sessile polyps have a dome-like shape and are attached directly to the colon or rectal wall. As a result, sessile polyps are harder to detect and require careful inspection. Pedunculated polyps have a stalk of variable length that connects the polyps to the walls of the colon or rectum. Lastly, sub-pedunculated polyps have a very short stalk and share similarities with both sessile and pedunculated polyps. 

Colonic adenomas can also be classified into different subtypes according to their growth pattern observed under a microscope. Villous features refer to finger-like or leaf-like protrusions, and depending on the percentage of villous features an adenoma has, it is classified into:

• Villous adenoma: has more than 75% of villous features and is usually flat 
• Tubulovillous adenomas: has between 25% and 75% of villous features
• Tubular adenomas: has less than 25% of villous features and is often pedunculated

In general, the size of the adenoma correlates with the amount of villous features it has. Tubular adenomas are on the smaller side of adenomas, measuring less than 1 cm. As the polyp increases in size, the villous features are more apparent. As a result, villous adenomas tend to have a larger polyp size.³ 

Tubular adenomas are the most common, accounting for more than 80% of diagnosed colonic adenomas.³ Tubulovillous adenomas are the second most common subtype, consisting of 10% to 15% of colonic adenomas. Lastly, villous adenomas are the least common, with a 5% to 10% prevalence.

Tubular adenomas and colorectal cancer

Studies from the late 1980s already showed that patients with colonic adenomas have an increased risk of developing colorectal cancer.⁵ There are two main pathways that lead to colorectal cancer: classic and alternate. 

The classic colorectal cancer formation model accounts for almost 80% of all colorectal cancer cases in the United States.³ Through this pathway, cancer arises from tubular or tubulovillous adenomas that are less than 1 cm in size. These then progress to villous adenomas bigger than 1 cm in size, which then progresses to colorectal cancer. This process is driven by the accumulation of different mutations and takes 10 to 15 years to develop.⁶ 

Until recently, tubular and tubulovillous adenomas were the only polyps thought to progress into colorectal cancer. However, research shows that some colorectal cancers arise through an alternate pathway that involves a different type of polyp known as sessile serrated polyps. 

Causes and risk factors for tubular adenomas

The exact cause of tubular adenomas is not well described. However, several factors associated with a higher risk of developing tubular adenomas have been identified, including:

• Older age
• Family history of polyps and colorectal cancer
• Lifestyle factors such as obesity, cigarette smoking, alcohol intake, and inactivity
• Genetic predisposition

Detection and diagnosis of tubular adenomas

Adenomas are usually asymptomatic. If a patient does develop symptoms, the most frequent symptom is finding painless bright or dark red blood when wiping after bowel movements. Other symptoms include weight loss, loss of appetite, abdominal pain, or changes in bowel movements, either diarrhoea or constipation.³

Since adenomas are mostly asymptomatic, they are found by chance during routine colorectal cancer screenings. In the United States, routine screening for polyps and colorectal cancer is recommended for people over the age of 50. Screenings include different types of exams, such as faecal occult blood tests and digital rectal examinations. However, the gold-standard method is colonoscopy, which is an exam that consists of inserting a flexible tube with an attached camera into the rectum. The camera allows the specialist to look inside the large intestine and detect irritated tissue, polyps, adenomas, and tumours. During a colonoscopy, a tissue sample (biopsy), polyps, and abnormal tissue can be removed. 

Before removing a polyp, it is hard to know whether it is precancerous or not. Therefore, when a polyp is detected during a colonoscopy examination, it is resected and examined under a microscope. When a specialist observes a polyp sample under a microscope, they can distinguish tubular adenomas from other polyps by looking at the size and shape of the cells and tissue. 

Treatment and management of tubular adenomas

If, during the colonoscopy, there is no polyp visible, the suggested time frame for a follow-up colonoscopy is within 10 years. However, if in the initial colonoscopy, a polyp is detected, the following colonoscopy is scheduled in the next 3 to 10 years, depending on the polyp size and specific features observed under the microscope:³

• If more than 10 adenomas are detected, a follow-up colonoscopy is recommended in less than 3 years.
• If 3 to 10 adenomas are detected, a follow-up colonoscopy is recommended after 3 years.
• If only 1 or 2 small tubular adenomas are detected, a follow-up colonoscopy is recommended after 5 to 10 years.

FAQs

What is the difference between tubular adenoma and colorectal cancer?

Tubular adenoma is a precancerous polyp. This means it is not cancerous, but could potentially evolve into colorectal cancer. Thus, by removing polyps you can prevent colorectal cancer development. 

What are the symptoms of tubular adenoma?

Most adenomas do not cause symptoms. Tubular adenomas do not usually bleed so it is hard to detect changes in the stool. This is why it is important to do routine colonoscopy screenings from the age of 50 onwards.

Can tubular adenomas be prevented?

It is possible to reduce the risk of developing tubular adenomas by making some lifestyle changes, such as not smoking cigarettes, reducing alcohol intake, and maintaining a healthy diet with less red meat and more fruits and vegetables. If you have a family history of polyps or colorectal cancer, your doctor might recommend screening at a younger age. 

What is tubular adenoma with low/high-grade dysplasia?

Dysplasia describes the changes in size, shape, and organisation of cells. All types of adenomas have some degree of dysplasia, as it becomes more severe (high grade), the risk of cancer increases.⁷ 

How long does it take for tubular adenoma to develop into cancer?

Research shows that tubular adenomas progress into colorectal cancer over the course of 10 to 15 years. However, it is important to note that less than 10% of tubular adenomas progress to colorectal cancer.⁶

What is the difference between a polyp and a tubular adenoma?

A polyp is an abnormal growth of tissue. An adenoma is a type of polyp that arises from glandular tissue. A tubular adenoma is a type of adenoma that when observed under a microscope has less than 25% of villous features. 

How often should you have a colonoscopy with tubular adenoma?

If only 1 or 2 small tubular adenomas are detected during a colonoscopy, a follow-up examination is recommended after 5 to 10 years. 

Summary

Tubular adenomas are abnormal growths in the walls of the colon or rectum. It is the most commonly diagnosed adenoma in the colon and is generally considered precancerous, meaning it can transform into colorectal cancer. Tubular adenomas are usually detected with a colonoscopy examination and are completely removed so they do not develop into cancer. Since tubular adenomas do not have any symptoms, it is important to follow recommended guidelines for routine screening of polyps and colorectal cancer.