Adenomas are common growths originating in the body’s glandular epithelial tissue. They are classified as benign tumors, meaning they are non-cancerous. They typically develop slowly and remain localized to the tissue where they began. Adenomas are a focus of preventative medicine due to their potential for change over time.
Defining Adenomas
An adenoma is a type of neoplasm, defined as an abnormal mass of tissue resulting from uncontrolled cell proliferation. Specifically, it is a benign growth that forms in the glandular epithelium, the thin layer of tissue lining organs and glands responsible for secretion. This tissue forms the lining of the digestive tract and components of glands such as the pituitary and adrenals.
The formation of an adenoma begins when an epithelial cell acquires genetic alterations, causing it to ignore normal regulatory signals for growth. This results in a localized, uncontrolled multiplication of cells, creating a distinct mass. Because adenomas are benign, their cells resemble normal glandular tissue and the growth remains confined to the original tissue layer. This non-invasiveness distinguishes an adenoma from a malignant tumor, or carcinoma.
Common Locations and Structural Types
Adenomas can arise in various organs, but they are most frequently found as polyps in the colon and rectum (colonic adenomas). Other common sites include the thyroid, adrenal, and pituitary glands. Adenomas in hormone-producing glands may cause symptoms by overproducing hormones, potentially leading to conditions like Cushing’s syndrome.
Colonic adenomas are classified into structural types based on their microscopic growth pattern. The most common type is the tubular adenoma, characterized by tube-shaped glands. Less common are villous adenomas, which exhibit long, finger-like projections, and tubulovillous adenomas, which contain a mixture of both features.
The structural type indicates the risk of progression. Tubular adenomas generally carry the lowest risk. Villous adenomas, due to their architecture, are associated with a greater likelihood of cellular changes and are considered higher risk. The size of the growth and the villous component are used to assess the overall health risk.
The Risk of Malignancy
The significance of adenomas lies in their potential to transform into malignant tumors, specifically adenocarcinomas. This progression is understood through the adenoma-carcinoma sequence, a slow, multi-step process involving the gradual accumulation of genetic mutations over many years. These mutations cause the cells to become increasingly abnormal.
A key concept in this process is dysplasia, which describes abnormal changes in the size, organization, and appearance of the cells within the adenoma. Dysplasia is graded based on severity: low-grade represents mild cellular abnormality, while high-grade indicates severe cellular disorganization and loss of normal tissue structure.
An adenoma with high-grade dysplasia is close to becoming invasive cancer, though the growth remains confined to the epithelial layer. Malignant transformation occurs when dysplastic cells breach the basement membrane, the structural barrier separating the epithelial lining from the tissue below. This breach allows cancerous cells to invade deeper layers and gain access to the circulatory or lymphatic systems. Although only a small percentage of adenomas progress to cancer, the vast majority of adenocarcinomas in the colon originate from a pre-existing adenoma.
Detection and Removal
Since most adenomas do not cause symptoms, especially when small, they are often discovered during routine screening procedures. For colonic adenomas, the primary detection method is colonoscopy, which allows a physician to visually inspect the entire inner lining of the large intestine. During this procedure, any growths, known as polyps, are identified and removed for laboratory analysis.
The standard treatment for most adenomas is prompt surgical removal, known as polypectomy. This procedure prevents malignant transformation and reduces cancer incidence. Small adenomas are typically removed using instruments passed through the colonoscope, while larger or more complex adenomas may require more involved surgical techniques.
Following removal, patients are placed on a surveillance schedule involving repeat colonoscopies to monitor for new growths. The frequency of these follow-up examinations is determined by a risk stratification system. This system considers factors such as the number and size of adenomas removed, and the presence of high-grade dysplasia or villous features. Ongoing surveillance ensures new adenomas are identified and removed before they progress to cancer.