An adenoma is a noncancerous (benign) growth made up of glandular cells — the specialized cells found throughout the body that produce and release substances such as mucus, enzymes, and hormones. Adenomas can develop in many different organs and are one of the most commonly diagnosed types of benign tumor. Although most adenomas are not cancerous, some types can develop into cancer over time. For this reason, they are often carefully monitored or removed when found, even if they are not causing symptoms.
Where do adenomas form?
Adenomas can form in any organ that contains glandular cells. They are most commonly found in the colon and rectum, where they are often called polyps, but they also occur in the stomach, thyroid gland, adrenal glands, salivary glands, breast, uterus (endometrium), and other locations throughout the body.
What are the most common types of adenomas?
The type of adenoma is named after the organ where it develops or its microscopic appearance. Some of the most commonly encountered adenomas include:
- Tubular adenoma — the most common type of colon polyp. Grows in a tube-like pattern and carries a low-to-moderate risk of becoming cancer.
- Tubulovillous adenoma — a colon polyp with both tubular and finger-like (villous) growth patterns. Carries a higher cancer risk than a purely tubular adenoma.
- Villous adenoma — a colon polyp made up almost entirely of finger-like projections. Carries the highest cancer risk among conventional colon adenomas and is always removed.
- Pleomorphic adenoma — the most common benign tumor of the salivary glands. Usually treated by surgical removal because it can slowly recur or, rarely, undergo malignant transformation.
- Fibroadenoma — a common benign breast tumor, particularly in younger women, made up of both glandular and fibrous tissue.
- Follicular adenoma — a benign tumor of the thyroid gland that typically does not require treatment unless it causes symptoms or grows large enough to affect thyroid function.
What is the difference between an adenoma and a polyp?
A polyp is a general term for any growth that projects from the lining of a hollow organ such as the colon, stomach, or uterus. Some polyps are adenomas — meaning they are made up of glandular cells — but others are made up of different cell types (such as inflammatory or hyperplastic polyps) and carry little or no cancer risk. When your report uses the word “adenoma,” it tells you specifically that the polyp is glandular in nature and may have some potential for becoming cancer.
Can an adenoma turn into cancer?
Most adenomas remain benign throughout a person’s lifetime. However, some types — particularly colon adenomas — can develop into cancer if left in place long enough. The risk depends on several factors that your pathologist will assess:
- Size — larger adenomas carry a higher cancer risk than smaller ones.
- Growth pattern — adenomas with a villous (finger-like) pattern carry a higher risk than those with a purely tubular pattern.
- Dysplasia — if the pathologist describes dysplasia (cells that look abnormal but are not yet cancer), this is a sign of increased cancer risk. High-grade dysplasia carries a higher risk than low-grade dysplasia.
- Location — adenomas in certain organs, such as the colon and endometrium, are more likely to progress to cancer than those in other locations.
This is why colon adenomas found during a colonoscopy are almost always removed at the time of the procedure — removing them prevents them from becoming cancerous.
Questions to ask your doctor
- What type of adenoma was found, and does it have any features that increase the risk of cancer, such as villous growth or high-grade dysplasia?
- Was it completely removed, and what do the margins show?
- What follow-up monitoring or testing is recommended?
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