A tubulovillous adenoma (TVA) is not cancer, but it is a serious precancerous condition. The term “polyp” describes any abnormal, mushroom-like growth extending from a mucous membrane, such as the lining of the colon or rectum. These growths are common, especially in people over the age of 50. Most polyps are benign, but a specific type known as an adenoma contains abnormal cells that can transform into malignancy over time. A TVA falls into this high-risk category, representing an intermediate form of growth that physicians must remove to prevent the development of colorectal cancer.
Understanding the Tubulovillous Adenoma
An adenoma is a type of neoplastic polyp, meaning it arises from the glandular tissue lining the colon, and it is characterized by abnormal cell growth called dysplasia. Adenomas are classified based on the architectural pattern of their cells when viewed under a microscope. A tubulovillous adenoma is defined by having a mixed structure, combining the features of both tubular and villous adenomas. The growth is typically found on the inner lining of the large intestine, including the colon and rectum, and represents about 10% to 25% of all adenomatous polyps encountered during screening.
The structure of a TVA is composed of two distinct parts: tube-shaped structures and finger-like projections. The tubular component consists of glands arranged in a branching pattern, which is the most common form of adenoma. The villous component is characterized by delicate, long, finger-like projections that extend outward from the polyp’s surface. For a polyp to be classified as a tubulovillous adenoma, the villous architecture must make up between 25% and 75% of the total growth.
The presence of this villous architecture makes the tubulovillous type a higher concern than a purely tubular adenoma. Villous adenomas, and therefore tubulovillous adenomas, tend to be larger in size, often exceeding one centimeter, and feature a sessile or flat growth pattern, making them more challenging to remove completely. This mixed cellular structure points to a greater accumulation of genetic mutations within the cells, placing the TVA further along the path toward malignancy compared to its tubular counterpart.
Assessing the Risk: Precancerous vs. Malignant
A tubulovillous adenoma is classified as a precancerous lesion, which means it is a non-invasive growth that contains abnormal cells with the potential to progress to invasive cancer. The distinction between a precancerous adenoma and a malignant tumor, or carcinoma, lies in whether the abnormal cells have broken through the basement membrane into the deeper layers of the bowel wall. While a TVA is confined to the inner lining, invasive carcinoma has penetrated the submucosa, gaining access to the lymphatics and blood vessels.
The degree of cellular abnormality within the adenoma is graded by pathologists as dysplasia. All adenomas exhibit some level of dysplasia, which is categorized as either low-grade or high-grade. Low-grade dysplasia involves cellular changes that are mild, localized, and relatively slow-growing, posing a lower immediate risk. High-grade dysplasia, conversely, indicates severe, disorganized, and aggressive cell abnormalities.
A diagnosis of high-grade dysplasia moves the adenoma significantly closer to becoming invasive cancer, representing the final stage before true malignancy develops. The risk of a TVA harboring or progressing to cancer is primarily linked to three factors: the size of the polyp, the proportion of villous architecture, and the grade of dysplasia. Adenomas larger than one centimeter, those with a higher villous component, and those with high-grade dysplasia are termed “advanced adenomas,” and they carry the greatest probability of malignant transformation.
Detection and Diagnostic Procedures
Tubulovillous adenomas rarely cause noticeable symptoms in their early stages, which is why they are most often discovered during routine colorectal cancer screening. The primary method for both detecting and diagnosing these growths is a screening colonoscopy. During this procedure, a flexible tube with a camera is inserted into the rectum and navigated through the entire colon, allowing a physician to visualize the inner lining and identify any suspicious polyps.
Once a growth is identified, the physician will typically remove the entire polyp, a process called polypectomy, or take a tissue sample, depending on the size and location of the lesion. The removed tissue is then sent to a pathology laboratory for detailed examination under a microscope. This is the only way to definitively diagnose the type of polyp and assess its malignant potential.
The pathologist’s report confirms the diagnosis of a “Tubulovillous Adenoma” by verifying that the tissue contains between 25% and 75% villous architecture. The report will also specify the grade of dysplasia found within the cells—low-grade or high-grade. This diagnostic confirmation is vital, as it determines the patient’s individual risk level and dictates the necessary schedule for future surveillance colonoscopies.
Treatment and Long-Term Surveillance
Because a tubulovillous adenoma is a high-risk precursor to colorectal cancer, immediate and complete removal is the standard course of treatment. For the majority of TVAs, this is accomplished endoscopically during the initial colonoscopy using a technique called polypectomy, where a snare or specialized instrument is used to excise the growth. For larger or flatter lesions that are more difficult to remove, a specialized technique like endoscopic mucosal resection (EMR) may be employed, which involves injecting fluid beneath the lesion to lift it for safer removal.
If the adenoma is very large, deeply invasive, or located in a technically challenging area, surgical resection may be necessary to ensure the entire lesion is cleared. Following the successful removal and confirmation of the diagnosis, the focus shifts to long-term surveillance. Patients who have had a TVA are considered to be at an elevated risk of developing new or recurrent adenomas in the future.
Current guidelines recommend a more frequent follow-up schedule for patients with high-risk adenomas, including those with tubulovillous features. For a completely removed TVA, the next surveillance colonoscopy is typically recommended in three years, rather than the standard ten-year interval used for the general population. This rigorous monitoring schedule is designed to detect any new adenomas or early recurrence promptly, significantly lowering the lifetime risk of developing invasive colorectal cancer.