A tubular adenoma is a type of polyp, or growth, that forms on the inner lining of the colon or rectum. The term “tubular adenoma” specifies both the type of tissue and the microscopic structure of the growth. These growths represent a significant precursor lesion in the development of colorectal cancer. Understanding tubular adenomas and the process of monitoring them is an important step in preventing cancer, which is why doctors recommend screening procedures to detect and remove these lesions.
Defining Tubular Adenomas
Adenomas are non-cancerous growths that develop from the glandular epithelial cells lining the colon and rectum. The term “tubular” describes the microscopic appearance of the cells, which are arranged in orderly, tube-like structures. Tubular adenomas are the most common type of adenoma found in the colon, representing the majority of all adenomatous polyps discovered during screening.
Although benign when first discovered, adenomas are classified as precancerous lesions because they have the potential to develop into cancer over time. A tubular adenoma is specifically classified if more than 80% of its structure consists of these tube-like glandular elements. This structure contrasts with villous adenomas, which have long, finger-like projections, and tubulovillous adenomas, which contain a mix of both features. Tubular adenomas are typically smaller than other adenoma types, often less than 1/2 inch in diameter, and tend to grow more slowly. Since most people are asymptomatic, these growths are usually found during routine screening procedures.
The Link to Colorectal Cancer Risk
Although a tubular adenoma is not cancer, it is a precancerous lesion that follows a recognized pathway toward cancer development. This progression, known as the adenoma-carcinoma sequence, moves from a normal cell to an adenoma, and finally to a carcinoma. Less than 10% of tubular adenomas become cancerous, but since nearly all colorectal cancers arise from pre-existing adenomas, their removal is the foundation of cancer prevention.
The risk of progression is determined by specific characteristics of the polyp. Larger size is a primary predictor of higher risk, as polyps 10 millimeters or larger have a greater chance of containing advanced cellular changes. Having three or more adenomas also increases the overall risk of advanced neoplasia (precancerous or cancerous changes).
The most specific biological risk factor is the degree of dysplasia, which describes how abnormal the cells look under a microscope. Low-grade dysplasia indicates mildly abnormal cells and carries a low risk of malignant transformation. High-grade dysplasia means the cells are significantly abnormal and appear closer to cancerous cells, raising the risk considerably. Small tubular adenomas (less than 10 millimeters) with low-grade dysplasia are classified as low-risk and have limited malignant potential.
Detection, Removal, and Follow-up Care
Tubular adenomas are most often discovered during a screening colonoscopy, which allows a doctor to visualize the entire inner surface of the colon. The patient follows a bowel preparation regimen beforehand to ensure the colon is clean for clear identification of polyps. The colonoscope, a flexible tube with a camera, is inserted, and growths are identified as small lumps protruding from the lining.
The standard treatment is removal, known as a polypectomy, which is typically performed immediately during the colonoscopy. The doctor uses specialized instruments, such as a wire snare or forceps, to detach the polyp from the colon wall. The removed tissue is sent to a pathology lab for detailed examination to confirm the diagnosis and assess risk factors like size and grade of dysplasia.
After removal, the patient enters a surveillance program with scheduled follow-up colonoscopies to monitor for new or recurrent polyps. The timing of surveillance is determined by the specific features of the removed adenoma. Patients with only one or two small tubular adenomas (less than 10 millimeters) showing low-grade dysplasia are typically considered low-risk, and current guidelines recommend their surveillance colonoscopy in seven to ten years.
Surveillance for High-Risk Patients
For individuals with high-risk findings, a shorter follow-up interval of approximately three to five years is generally recommended. High-risk findings include:
- An adenoma 10 millimeters or larger.
- Three or more adenomas.
- Any adenoma with high-grade dysplasia.
Adhering to this personalized surveillance schedule is the primary way to ensure any new growths are found and removed before they progress to cancer.