A tubulovillous adenoma is a precancerous polyp found in the colon or rectum that contains a mix of two growth patterns: tube-shaped glands and finger-like projections. It sits between the two other types of adenomatous polyps in terms of cancer risk, carrying a higher risk than purely tubular adenomas but lower than purely villous ones. Most people learn they have one after a routine colonoscopy, since these polyps rarely cause symptoms on their own.
How It Looks Under a Microscope
Pathologists classify colon polyps by their internal architecture. Tubular adenomas are made up of small, round, tube-like glands. Villous adenomas have tall, finger-like projections that resemble the fronds of a fern. A tubulovillous adenoma has both patterns. The standard threshold for this diagnosis is that roughly 25% to 75% of the polyp’s surface shows villous architecture. Below 25% villous, it’s classified as tubular. Above 75%, it’s called villous.
Every adenomatous polyp, including tubulovillous adenomas, shows some degree of dysplasia, meaning the cells are growing in an irregular, disorganized pattern. Dysplasia is graded as either low-grade or high-grade. Low-grade dysplasia reflects early, mild cellular changes. High-grade dysplasia means a more serious precancerous transformation is underway and warrants closer follow-up.
Symptoms and How They’re Found
Most tubulovillous adenomas cause no symptoms at all. They grow slowly and are typically discovered during a screening colonoscopy before they cause any noticeable problems. This is one of the key reasons routine screening is so effective at preventing colorectal cancer: it catches these polyps while they’re still silent.
In some cases, particularly when a polyp is large, it can cause small amounts of blood in the stool, changes in bowel habits like new constipation or diarrhea, changes in stool shape, or abdominal discomfort. These signs overlap with many other conditions, so they aren’t specific to polyps, but they do warrant evaluation.
Where They Tend to Grow
Tubulovillous adenomas can appear anywhere in the colon or rectum, but they have a preference for the lower end of the digestive tract. In a review of 65 large villous and tubulovillous adenomas (4 cm or greater), 55% were found in the rectum and 15% in the sigmoid colon. About 23% were in the cecum, the pouch at the beginning of the large intestine. This rectal predominance is consistent with the broader pattern of villous-type polyps favoring the distal colon.
Cancer Risk
A tubulovillous adenoma is not cancer, but it is considered a significant precancerous finding. The villous component is what drives the concern. Polyps with more villous tissue have a higher likelihood of eventually progressing to adenocarcinoma, the most common type of colorectal cancer. Mayo Clinic classifies the cancer risk of tubulovillous adenomas as “high” if they are not removed.
Several factors influence how risky a specific polyp is. Size matters: larger polyps are more likely to harbor cancer or progress to it. High-grade dysplasia is another red flag, indicating the cells are closer to becoming malignant. The combination of villous features, large size, and high-grade dysplasia puts a polyp in the highest risk category.
At the genetic level, certain mutations are more common in tubulovillous adenomas than in purely tubular ones. One study in the British Journal of Cancer found that mutations in the KRAS gene, which helps regulate cell growth, were present in about 41% of tubulovillous adenomas compared to just 6% of tubular adenomas. These mutations are part of the step-by-step genetic progression from normal tissue to polyp to cancer.
How They’re Removed
The standard approach is to remove a tubulovillous adenoma during the same colonoscopy in which it’s discovered. The gastroenterologist uses a wire loop, a snare, or other instruments passed through the endoscope to cut away the polyp. For most polyps, this is straightforward and requires no additional procedures.
Surgery becomes necessary when a polyp can’t be fully removed through the endoscope. This happens when the polyp is in a hard-to-reach location, when it’s too large or shaped in a way that prevents complete endoscopic removal, or when there’s suspicion of cancer that has invaded deeper tissue layers. If a polyp shows signs of deeper invasion during the procedure (for example, if it doesn’t lift away from the underlying tissue as expected), that raises concern for malignancy and typically shifts the approach toward a formal surgical resection.
When a removed polyp turns out to contain early cancer on pathology review, the decision about whether additional surgery is needed depends on specific features: how deeply the cancer invaded, how abnormal the cells look, and whether cancer cells were found near blood vessels or lymphatic channels. If these features are all favorable, the endoscopic removal may be sufficient. If not, surgical resection of that segment of colon is the next step.
Follow-Up Colonoscopy Schedule
Because tubulovillous adenomas carry villous features, they place you in a higher surveillance category than a small, simple tubular adenoma would. Current U.S. guidelines recommend your next colonoscopy in 3 years if your polyp had villous features, was 1 cm or larger, or showed high-grade dysplasia. A tubulovillous adenoma checks at least one of those boxes by definition.
If that 3-year follow-up colonoscopy comes back completely normal with no new polyps, the interval for the next one extends to 5 years. After that, if results continue to be clean, your doctor may gradually lengthen the interval further. The goal of this schedule is to catch any new polyps early, before they have a chance to progress. People who have had one adenoma with villous features are at increased risk of developing more adenomas in the future, which is why ongoing surveillance is important even after successful removal.
Tubulovillous vs. Other Polyp Types
- Tubular adenoma: The most common type of adenomatous polyp. Made up almost entirely of tube-shaped glands, with less than 25% villous tissue. Carries the lowest cancer risk of the three adenoma types, though it still requires removal and follow-up.
- Tubulovillous adenoma: A mix of tubular and villous patterns (25% to 75% villous). Intermediate cancer risk. Accounts for a smaller share of adenomas than the purely tubular type.
- Villous adenoma: More than 75% villous architecture. Highest cancer risk among the three types. These polyps can sometimes secrete enough mucus and fluid to cause diarrhea or electrolyte imbalances, particularly when large.
All three are part of the adenoma-to-carcinoma sequence, the well-established pathway through which normal colon tissue accumulates genetic changes, forms a polyp, and can eventually become cancer. Finding and removing any adenoma interrupts that sequence.