Precancerous polyps are abnormal growths in the colon or rectum that have the potential to turn into cancer. Not all precancerous polyps will become cancerous, but removing them is important to prevent colon cancer. Here we look at the likelihood of precancerous polyps becoming cancerous.
What are precancerous polyps?
Precancerous polyps, also known as adenomas, are growths that form on the lining of the colon or rectum. They are benign (noncancerous) clumps of cells that form as tube-like or mushroom-like growths. There are several types of precancerous polyps:
- Tubular adenomas – Grow on small stalks like mushrooms and account for about 80% of precancerous polyps.
- Tubulovillous adenomas – Have features of both tubular and villous adenomas.
- Villous adenomas – Grow with finger-like projections and make up 10-15% of precancerous polyps. They have a higher risk of becoming cancerous.
- Sessile serrated adenomas – Flat, precancerous lesions that develop in the lining of the colon.
Adenomatous polyps are the most common type and have gland cells that look abnormal but are not cancerous yet. Over time, some of the abnormal cells in adenomas can slowly turn into colon cancer cells.
What percentage of precancerous polyps become cancerous?
It is estimated that only about 5-10% of all precancerous colorectal polyps will eventually progress to colon cancer if left untreated. Some key statistics on precancerous polyps becoming cancer include:
- About 30-50% of adults over 50 years old have precancerous polyps in their colon.
- Less than 10% of small (less than 1 cm) adenomatous polyps become cancerous.
- About 10-25% of larger (1 cm or greater) adenomas may become cancerous.
- The risk of cancer is related to the size of the polyp – the larger the polyp, the higher the risk of cancer developing.
- Villous adenomas have a greater risk with up to 40% becoming cancerous eventually.
- It can take 5-15 years for a precancerous polyp to develop into colorectal cancer.
So while most polyps will not become cancer, regular screening and removal of polyps is important to prevent cancer from developing.
Risk Factors for Precancerous Polyps Becoming Cancerous
There are certain risk factors that can increase the likelihood of a precancerous polyp progressing to cancer:
- Size – Larger polyps (over 1 cm) have a higher risk of becoming cancerous.
- Number – People with more than 2-3 polyps are at increased risk.
- Type – Villous adenomas and sessile serrated polyps have a higher cancer risk.
- Dysplasia – Polyps with high-grade dysplasia (abnormal cells) are more likely to progress.
- Family history – Having a family history of colon cancer increases risk.
- Age – Older age increases the risk of cancerous progression.
People who have these risk factors may need more frequent colonoscopy screening or removal of any polyps found.
Factors that Lower the Risk of Progression
While some polyps have a higher inherent risk, there are also factors that can lower the chances of a precancerous polyp becoming cancerous:
- Removal of polyps – Taking out polyps prevents further progression.
- Small size – Polyps less than 5mm have a very low cancer risk.
- No dysplasia – Polyps without abnormal looking cells are less risky.
- Tubular adenoma type – Compared to villous, this type is lower risk.
- Youth – Precancerous polyps in younger adults are less likely to progress before next colonoscopy.
By removing precancerous polyps early and monitoring with regular follow-up colonoscopies, the likelihood of progression to cancer is greatly reduced.
How Often to Get Colonoscopies to Remove Polyps
Most major health organizations recommend regular colon cancer screening with colonoscopies beginning at age 45-50 for average-risk adults. Those with a family history or other risk factors should start screening earlier.
The recommended interval for repeat colonoscopy screening depends on the findings of your initial colonoscopy:
| Colonoscopy Findings | When to Repeat Colonoscopy |
|---|---|
| No polyps | Every 10 years |
| Small (less than 10mm) hyperplastic polyps | Every 10 years |
| 1-2 small (less than 10mm) tubular adenomas with no dysplasia | 5-10 years |
| 3-10 adenomas or any adenoma >10mm | 3 years |
| More than 10 adenomas | Less than 3 years |
| Adenoma with villous features or high-grade dysplasia | 3 years |
| Sessile serrated polyp(s) without dysplasia | 3-5 years |
| Sessile serrated polyp(s) with dysplasia | 3 years |
Your doctor may recommend more frequent colonoscopies if you have polyps that have a higher risk of becoming cancerous or if there is uncertainty from the initial colonoscopy.
Can Precancerous Polyps Go Away on Their Own?
Precancerous polyps will not usually disappear on their own without removal. They will typically continue to grow larger over time if left untreated. One study found that untreated polyps grew by around 2-3 mm per year.
Very small polyps (1-3 mm) that are not pre-cancerous (hyperplastic polyps) can sometimes disappear on follow up colonoscopy. But precancerous adenomas will rarely go away without being removed.
Getting a colonoscopy to take out polyps is recommended since polyp removal can prevent up to 90% of future colon cancers.
Are There Options Other Than Surgery to Remove Polyps?
Colonoscopy is the main method used to detect and remove precancerous polyps in the colon. During the procedure, the doctor can pass instruments through the colonoscope to safely excise polyps.
There are some alternative methods being studied but they are not commonly used yet:
- MED – A miniature colonoscopy device (MED) can be swallowed like a pill and takes internal images as it passes through the GI tract. Polyps can then be removed later by standard colonoscopy.
- Cytosponge – This is a sponge on a string device that can collect cells from the lining of the esophagus. It is being researched to sample cells in the colon to detect precancerous changes.
- Forthcoming alternative methods – Researchers are looking at other potential techniques like vault nanoparticles and magnetized pills to help recognize and remove polyps without colonoscopy.
But for now, traditional surgical polyp removal with colonoscopy remains the gold standard. Medications and nonsurgical methods are not ready yet for routine treatment of precancerous colon polyps.
What Happens If You Leave Precancerous Polyps?
Leaving precancerous polyps in place instead of removing them can allow some polyps to eventually progress to colon cancer. Here is what can happen with untreated polyps:
- Adenomatous polyps can continue to grow larger, with a higher chance of becoming cancerous over time.
- Villous adenomas in particular may develop into cancer more quickly than other types of polyps.
- Polyps with high-grade dysplasia (most abnormal looking cells) have the highest risk of advancing to cancer.
- Even polyps without dysplasia can eventually develop concerning cellular changes.
- Every year polyps are left untreated, the risk of cancer increases.
- Advanced adenomas left for 5-10 years can progress to colon cancer, usually beginning with cellular changes indicative of cancer.
That’s why removing precancerous polyps is critical for colon cancer prevention. Taking polyps out disrupts the cancer process before it can advance too far.
Takeaways
In summary, here are the key points to understand about precancerous polyps becoming cancerous:
- About 5-10% of adenomatous colon polyps will progress to cancer if left untreated.
- Larger polyps, villous polyps, and polyps with dysplasia have the highest risk of becoming cancerous.
- Prompt removal of polyps by colonoscopy is recommended to prevent cancer.
- Patients with precancerous polyps require regular surveillance colonoscopies based on the type and number of polyps.
- Most polyps can be removed safely via colonoscopy once detected through screening.
- Leaving polyps untreated allows cellular changes to progress, increasing cancer risk over time.
Talk to your doctor about getting screened for colon polyps starting at age 45-50. Finding and removing any precancerous polyps early provides excellent colon cancer prevention and reduces your risk of developing life-threatening colon cancer in the future.