A precancerous polyp is an abnormal growth of tissue that forms on the lining of the colon or rectum. Polyps are quite common, especially as people get older. Most polyps are benign (noncancerous), but some polyps can eventually turn into cancer if not removed. These abnormal growths are called precancerous polyps or adenomas. Detecting and removing precancerous polyps is one of the main goals of colon cancer screening.
What is a precancerous polyp?
A precancerous polyp, also called an adenomatous polyp or adenoma, is a benign growth that has the potential to become cancerous over time. Adenomas form on the lining of the colon or rectum when healthy cells mutate and begin to multiply abnormally. While most adenomas will never become cancer, the longer they remain in the colon, the higher the risk they will turn into colon cancer. That’s why it’s recommended to have them removed.
Types of precancerous polyps
There are different classifications of precancerous polyps:
- Tubular adenoma – Most common, smooth mushroom shape, low risk of cancer
- Tubulovillous adenoma – Larger with more villi, higher cancer risk
- Villous adenoma – Least common, look like fronds, highest risk of cancer
- Sessile serrated adenoma – Flat and pale, can quickly become cancerous
The type of adenoma provides information about how likely it is to progress to cancer. In general, the more villous features an adenoma has, the more likely it is to become cancerous. Villous adenomas in particular have a high risk of malignancy.
What does a precancerous polyp look like?
Precancerous polyps can vary greatly in size, shape, and appearance. Here are some of the common characteristics:
Size
Polyps can range from a few millimeters to several centimeters in size. Larger polyps over 1 cm have a higher potential of becoming cancerous. The majority of precancerous polyps are small, less than 1/2 inch.
Shape
Polyps come in different shapes:
- Sessile – Broad, flat base attaching to the bowel wall
- Pedunculated – Mushroom-like with a stalk connecting it to the bowel lining
- Semipedunculated – Intermediate features between sessile and pedunculated
Pedunculated polyps have less direct contact with the bowel lining and are less likely to be precancerous compared to sessile polyps.
Color
Most precancerous polyps are pink to red in color with a mucus coating. They are often the same color as surrounding healthy tissue. However, some types may appear pale or even whitish.
Surface
The surface of an adenoma can be smooth, lobulated, ulcerated, or irregular. Villous adenomas often have small frond-like projections. Irregular surface patterns increase the likelihood of dysplasia and malignancy.
Location
Precancerous polyps can occur anywhere in the colon and rectum but are most common in the sigmoid colon and rectum. Polyps that form on the right side of the colon are associated with a higher risk of becoming cancerous.
How to identify precancerous polyps
Most small adenomas do not cause any signs or symptoms. The only way to accurately identify precancerous polyps is through screening tests like a colonoscopy. During a colonoscopy, a doctor can see the entire lining of the colon and remove any abnormal growths for biopsy.
Some potential signs that may lead to diagnosis of precancerous polyps include:
- Rectal bleeding
- Blood in the stool
- Changes in bowel habits
- Unexplained iron deficiency anemia
- Abdominal pain or discomfort
- Narrowed stool caliber
While many conditions can cause these symptoms, it is important to follow up with a doctor to rule out potentially serious causes like precancerous polyps.
Risk factors
Certain factors increase the likelihood of developing adenomas and colorectal cancer:
- Being over age 50
- Family history of colon polyps or colon cancer
- Inflammatory bowel diseases like ulcerative colitis or Crohn’s
- Type 2 diabetes
- Obesity
- Smoking
- Heavy alcohol use
- Low-fiber, high-fat diet
- Sedentary lifestyle
Talk to your doctor about getting screened if you have any of these risk factors. The earlier precancerous polyps are found, the better the chances of preventing cancer.
What are the stages of polyp development?
It can take 5-15 years for a precancerous polyp to develop into colorectal cancer. Polyps go through different stages of advancement on their way to becoming cancerous:
| Stage | Description |
|---|---|
| Aberrant crypt foci | Earliest lesions, involving a small collection of abnormal gland cells in the colon lining |
| Adenomatous polyp | Benign precancerous polyp with dysplasia |
| Advanced adenoma | Larger polyp (over 1 cm) with villous features or high-grade dysplasia |
| Carcinoma in situ | Cancer cells confined to epithelium lining without invasion |
| Invasive colorectal cancer | Cancer cells spread below the mucosal lining into deeper layers |
Removing polyps in the early stages interrupts this progression and prevents cancer.
How are precancerous polyps treated?
The standard treatment for precancerous polyps is endoscopic removal, most often during colonoscopy. There are several methods that gastroenterologists can use:
Polypectomy
The most common way to remove polyps is by passing a wire loop through the colonoscope to cut the polyp from the lining. The polyp can then be safely withdrawn from the body.
Endoscopic mucosal resection
Some larger polyps are removed by resection, which cuts deeper into the bowel lining surrounding the polyp. This helps ensure none of the abnormal cells are left behind.
Endoscopic submucosal dissection
For large sessile polyps, dissection may be done by injecting fluid beneath the polyp to separate it from the submucosa for complete removal.
For the majority of polyps, endoscopic removal is curative and no additional surgery or treatment is required. Biopsy results determine if more monitoring or surgery is needed. Some cases of invasive cancer or certain polyp types warrant surgery to remove a portion of the colon.
What happens after polyp removal?
Patients who have had precancerous polyps removed will need ongoing colonoscopy surveillance. How often you need follow-up depends on:
- Number of polyps
- Size of polyps
- Polyps with villous features or high-grade dysplasia
- Number of polyps completely excised
Follow-up is typically recommended:
- Within 3 years if 1-2 small tubular adenomas are removed
- Within 3 years if one adenoma with villous features or high-grade dysplasia is removed
- Within 1 year if more than 2 adenomas are removed
- Within 1 year if polyps could not be fully removed
Close surveillance helps detect and remove any new polyps before they potentially become cancerous.
Can I prevent precancerous polyps?
While some polyps are impossible to prevent completely, adopting healthy lifestyle habits can reduce your risk:
- Eat a diet high in fiber, fruits and vegetables
- Limit red and processed meats
- Maintain a healthy weight
- Exercise regularly
- Don’t smoke
- Limit alcohol
- Take aspirin if recommended by your doctor
Get screened for colon cancer starting at age 45, or earlier if you have risk factors. Finding and removing precancerous polyps early is the best way to prevent colon cancer. Talk to your doctor about what screening option is right for you.
Conclusion
Precancerous polyps are growths in the colon that can develop into cancer over time. They are usually small and produce no symptoms initially. Adenomas may become cancerous if allowed to grow, which is why removing them is so important. The characteristics of polyps, including their size, shape, and microscopic appearance, provide clues about their likelihood of progressing to cancer. Regular screening tests allow polyps to be found and removed early, before they ever become cancerous. Ongoing surveillance colonoscopies are needed after polyp removal to look for new abnormalities. Leading a healthy lifestyle may help reduce the chances of developing colorectal polyps and cancer in the first place. Being aware of your own risk and talking to your doctor can help you take control of your colon health.