What Are The Types Of Adenomas

Introduction

An adenoma is a benign (non-cancerous) tumour found in the glandular tissues of the body. Though an adenoma is a non-cancerous growth, it has the potential to transform into an adenocarcinoma - a type of cancerous growth. Adenocarcinomas account for most types of cancers in the body.¹ 

Some organs where adenomas can be found include the colon, duodenum, brain, breast, thyroid, lung, kidneys, adrenal gland, pancreas, prostate, uterus, and liver.²

Adenomas can be classified into three types depending on their microscopic appearance; tubular, villous or tubulovillous. The different types of adenomas have varying risks of developing into cancer so it is important to seek advice from your healthcare provider if you are concerned about any of your symptoms.³ 

Types of adenomas

Tubular adenomas

This subtype of adenoma is the most common of the three. Tubular adenomas are usually smaller and are formed mostly from a network of glands. 

Villous adenomas

Villous adenomas are often referred to as having finger-like projections, though they may also exhibit some tubular features. An adenoma is classed as villous if it exhibits more than 75% of villous features. They have the highest risk of becoming cancerous and are typically larger than the other types of adenomas. 

Tubulovillous adenomas

The third type of adenoma has both tubular and villous features. Under a microscope, tubulovillous adenomas have between 25% to 75% of villous characteristics.⁴

Differences among types of adenomas

Cell composition

Adenomas are composed of abnormal epithelial cells. Epithelial cells form the lining of the entire body and its organs. Part of the epithelium is composed of glandular cells. Glands secrete important substances into the body such as mucus, enzymes and hormones.⁵

Appearance

If normal cells become dysplastic, they can transform into cancer cells. Dysplasia is when cells possess an abnormal microscopic appearance. Dysplasia is always present to some degree in adenomas and can be low-grade - where there are more normal cells compared to abnormal cells, or high-grade. High-grade dysplasia is where there are more atypical cells than normal cells. Dysplasia can progress to adenocarcinoma.⁴

Some larger adenomas may be visible without a microscope. If they are pedunculated i.e. they protrude into a hollow cavity via a stem, such as in the bowel, they are referred to as adenomatous polyps. Polyps can be found in the nose, colon, rectum, uterus and other organs of the body and can be visualised with a camera operated by a medical professional. Adenomatous polyps can be sessile or serrated. If the polyp has a wider base and flatter appearance, it’s referred to as sessile. Serrated polyps have a sawtooth-like appearance under a microscope.³

Risk of progression to cancer

Not all adenomas progress to cancer. As mentioned previously, tubular adenomas have a lower likelihood of becoming cancerous compared to villous adenomas. If an adenoma becomes severely dysplastic and breaches the area it originates from, it becomes cancerous. 

The risk of progression to cancer depends on several factors, including the type of adenoma, genetics and other environmental factors. Bowel cancers, for example, typically develop from precancerous polyps in the large intestine or rectum. The time taken for these adenomas to progress into cancer is usually many years. However, in people with more risk factors, this sequence of transformation from adenomatous polyp to cancerous tumour can occur much quicker. This is true in conditions such as familial adenomatous polyposis (FAP). It is a genetic disorder that can be present in several members of the same family. Those who are affected almost always develop bowel cancer before 40 years of age unless treated sooner.⁶

In the brain, pituitary adenomas can be found in the pituitary gland and cause hormonal issues, though they rarely progress to cancer.⁷

Diagnosis and treatment

Screening

Adenomas are not always symptomatic. This means you could have one and not know. For this reason, screening programs such as those for breast, cervical and bowel cancers exist. Screening involves testing certain groups of people for a disease which they don’t have symptoms of but may be at risk of developing. These programmes are designed to identify precancerous adenomas and cancers, including adenocarcinomas, in the earlier stages, where treatment is more likely to be successful.

A colonoscopy, which is a camera test to check for abnormalities in the bowels, is part of a screening programme to detect bowel cancer. This is usually performed after a positive faecal-occult blood test (FIT) result. For this test, a small sample of faeces is taken to check for blood which is not visible to the naked eye. Your healthcare provider may also perform a physical exam to check for rectal polyps and rectal bleeding before referring you for further testing.⁶

Other screening programmes include those for breast and cervical cancer. Programmes will vary depending on which country you reside in. 

Those identified to be at higher risk of certain cancers e.g. those with a genetic predisposition to a disease, may be invited for screening from an earlier age in comparison to the general population.

If you have any concerning or unexplained symptoms, you should not wait to be invited to a screening appointment. Instead, contact your healthcare provider urgently so that they can begin the process of diagnosis and recommend the most appropriate treatment. 

Removal of adenomas

If you are found to have an adenoma, your healthcare provider will advise the best course of action moving forward. 

Sometimes, a biopsy - a small sample of tissue from the area - is first taken to assess the microscopic appearance of the cells. This will help to determine the need for surgery. 

In adenomas that have a higher risk of progressing to cancer, surgical removal may be recommended to reduce your risk. This is usually the case for all colonic polyps during a colonoscopy so that the tissues can be properly examined under a microscope.⁴

Further testing may also be advised depending on the appearance of the cells in the tissue removed during surgery. If cancer has been found, your healthcare provider should produce a tailored treatment and surveillance plan with you.

Summary

Many people develop adenomas and are unaware of their presence in the body. Though non-cancerous, they still pose the threat of becoming cancerous over time.  If you are concerned that any symptoms you may be experiencing are related to an adenoma or adenocarcinoma, speak to your doctor.