A sigmoid colon polyp is a small growth that protrudes from the inner lining of the sigmoid colon, the S-shaped section of your large intestine just before the rectum. Most sigmoid polyps are harmless and cause no symptoms, but some types can slowly develop into colorectal cancer if left in place, which is why they’re routinely removed during colonoscopy.
Where the Sigmoid Colon Sits
Your large intestine ends with a curved, S-shaped segment that connects the descending colon to the rectum. This is the sigmoid colon, and it sits in the lower left side of your abdomen. It’s part of what doctors call the “left” or “distal” colon, and it’s one of the most common locations where polyps and colorectal cancers develop. Larger adenomas, the type most likely to become cancerous, tend to cluster in this left-sided region.
Types of Sigmoid Polyps
Not all polyps carry the same risk. The type of cells inside the polyp determines whether it could become dangerous, and a pathologist identifies this after the polyp is removed and examined under a microscope.
Adenomatous Polyps
These are the ones doctors watch most closely because they can progress to cancer over time. About 80% of adenomatous polyps are tubular adenomas, which have a relatively organized internal structure and lower cancer risk. Another 5 to 15% are villous adenomas, which have a more complex, finger-like architecture and carry a higher risk. The remaining 5 to 15% are tubulovillous, a mix of both patterns. All adenomatous polyps gradually develop abnormal cell changes that distinguish them from harmless growths.
Hyperplastic Polyps
These are non-neoplastic, meaning they don’t follow the pathway toward cancer. Hyperplastic polyps in the rectum and sigmoid colon are generally considered low risk. When found in this location and under 10 mm, they typically require only routine follow-up.
Sessile Serrated Lesions
These polyps have a saw-tooth pattern under the microscope and sit flat against the colon wall rather than growing on a stalk. They’re more commonly found in the right (proximal) colon, but they can appear anywhere. Without abnormal cell changes, their cancer risk is low. If a pathologist finds dysplasia (precancerous changes), however, the risk becomes significant.
How Size Affects Cancer Risk
Polyp size is one of the strongest predictors of whether a growth contains cancer cells. The numbers are striking: polyps under 10 mm have a malignancy rate of less than 1%. Once a polyp exceeds 10 mm, that rate jumps to about 14%. At 20 mm or larger, roughly 1 in 4 polyps contains cancerous tissue, and at 30 mm the rate climbs to around 30%.
This is why the size noted on your colonoscopy report matters. A 3 mm polyp found in the sigmoid is a very different clinical situation than a 25 mm one, even if both are adenomas.
The Adenoma-to-Cancer Timeline
Adenomatous polyps don’t become cancerous overnight. The progression from a small adenoma to colorectal cancer is estimated to take years, sometimes a decade or more, which is exactly why screening colonoscopy works so well. Catching and removing polyps during this slow window prevents cancer from ever developing.
For advanced adenomas (those that are large, have villous features, or show high-grade precancerous changes), the annual transition rate to cancer increases with age. In people aged 55 to 59, the rate is about 2.6% per year. By age 80 and older, it rises to roughly 5% per year. Over a 10-year span, an advanced adenoma left untreated in a 55-year-old has about a 25% chance of becoming cancerous, rising to over 40% in someone aged 80.
Symptoms You Might Notice
Most people with sigmoid colon polyps have no symptoms at all. That’s the whole reason screening programs exist: polyps are typically silent until they’re large or already cancerous.
When symptoms do appear, the most common is rectal bleeding. You might see blood on toilet paper, in the toilet bowl, or mixed into your stool. Blood from the sigmoid colon can appear as bright red streaks or occasionally make stool look darker. Over time, chronic low-level bleeding from a polyp can lead to iron deficiency anemia, leaving you feeling unusually tired or short of breath without an obvious cause.
Risk Factors for Developing Polyps
Six lifestyle factors have been independently linked to polyp development: cigarette smoking, obesity (a BMI of 30 or higher), high red meat intake, low fiber intake, low calcium intake, and not regularly using anti-inflammatory pain relievers like aspirin or ibuprofen. Higher intakes of fiber, calcium, and folate are all associated with significantly lower polyp risk. Smoking stands out as a particularly strong factor, with risk increasing alongside the number of pack-years smoked.
Inherited conditions like familial adenomatous polyposis and Lynch syndrome dramatically increase polyp and cancer risk, but these are relatively rare. For most people, polyps develop sporadically as a result of aging combined with lifestyle factors.
How Sigmoid Polyps Are Removed
Polyps found during a colonoscopy are almost always removed on the spot, a procedure called polypectomy. The technique your doctor uses depends on the polyp’s size and shape.
Very small polyps (1 to 3 mm) are typically grabbed and removed with tiny forceps passed through the colonoscope. For slightly larger polyps, doctors use a wire loop called a snare, which is placed around the base of the polyp and tightened to cut it free. Small polyps are often removed with a “cold” technique (no electrical current), while larger polyps may require electrocautery to cut through the tissue and seal blood vessels simultaneously. Flat polyps that sit flush against the colon wall can be trickier to snare, and your doctor may use a barbed snare or inject fluid beneath the polyp to lift it before removal.
For large polyps (10 mm or bigger), removal sometimes has to be done in pieces, a technique called piecemeal resection. This is still performed through the colonoscope and doesn’t require surgery in most cases.
Recovery After Polyp Removal
Most people go home the same day and resume normal activities within 24 hours. The main complication to be aware of is bleeding, which occurs in roughly 0.3% to 6% of polypectomies depending on polyp size and technique. Bleeding can happen immediately or be delayed, showing up on average 5 to 7 days later, though it can occur up to 30 days after the procedure.
The risk tracks closely with polyp size. For polyps under 10 mm, delayed bleeding happens in about 1% of cases. For polyps over 20 mm, the rate rises to about 6.5%. If you notice significant rectal bleeding, dark stools, or feel lightheaded in the weeks following your procedure, contact your doctor.
Follow-Up Surveillance Schedule
Your colonoscopy report and pathology results together determine when you’ll need your next screening. The schedule is based on polyp type, size, and number.
- 1 or 2 small tubular adenomas (under 10 mm): Follow-up in about 5 years, sometimes with a stool-based test rather than a full colonoscopy.
- 3 or 4 small tubular adenomas: Colonoscopy in 5 years.
- 5 to 10 adenomas, any adenoma 10 mm or larger, or adenomas with villous features or high-grade precancerous changes: Colonoscopy in 3 years.
- More than 10 adenomas on a single exam: Colonoscopy in 1 year, with possible genetic counseling.
- Small hyperplastic polyps in the sigmoid or rectum: Considered low risk, with follow-up at standard 5-year intervals.
- Large polyps removed in pieces (20 mm or bigger): A check at the removal site in 6 months, then colonoscopy at 1 year, then again at 3 years if the site looks clear.
These intervals exist because new polyps can form over time, and people who’ve had adenomas are at higher risk for developing more. Sticking to the recommended surveillance schedule is one of the most effective ways to prevent colorectal cancer.