Understanding Colon Polyp Size, Cancer Risk, and Advanced Detection Methods

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• Polyp Size and Cancer Risk
• Clinical Significance of Different Polyp Sizes
• Flat Adenomas Explained
• Serrated Adenomas: A Second Cancer Pathway
• CT Colonography for Polyp Detection
• Screening Guidelines and Importance
• Full Transcript

Polyp Size and Cancer Risk

Polyp size is a critical factor in determining cancer risk in the large bowel. Dr. Perry Pickhardt, MD, states that size is "actually everything in terms of polyp importance." These precancerous growths develop over many years before potentially transforming into colorectal cancer. The larger a polyp becomes, the greater its chance of harboring advanced precancerous changes or early cancer.

Clinical Significance of Different Polyp Sizes

Polyps are categorized by size, which dictates clinical management. Dr. Perry Pickhardt, MD, defines diminutive polyps as those 5 millimeters and smaller. These tiny lesions have "almost zero chance of being cancer" and are too common to remove aggressively. Large polyps, measuring 10 millimeters (1 cm) and larger, are the primary target for screening and prevention. The vast majority of advanced adenomas fall into this large size category.

The intermediate, or "gray zone," includes polyps sized 6 to 9 millimeters. Dr. Perry Pickhardt, MD, notes there is some controversy around these. They are more common than large polyps but less common than diminutive ones. In his practice, Dr. Perry Pickhardt, MD, advises removal of all polyps 6 mm and greater, though many patients opt for surveillance at three-year intervals to monitor for growth.

Flat Adenomas Explained

Flat adenomas are a specific and important type of colon polyp. Dr. Anton Titov, MD, and Dr. Perry Pickhardt, MD, discuss how these lesions are more difficult to detect than obvious, protruding polyps. Contrary to some beliefs, Dr. Pickhardt clarifies that flat adenomas are "much less aggressive on average" and "grow very slowly." This slow growth means there is more time to detect them during routine follow-up screenings.

Serrated Adenomas: A Second Cancer Pathway

Serrated adenomas represent a distinct pathway to colon cancer development. Dr. Perry Pickhardt, MD, explains that these lesions account for an estimated 10-15% of colon cancers. Serrated adenomas tend to be flat and are often located in the right side of the colon. The good news, according to Dr. Pickhardt, is that CT colonography demonstrates "very good accuracy" in detecting these serrated lesions, which is crucial for intercepting this cancer pathway.

CT Colonography for Polyp Detection

CT colonography, also known as virtual colonoscopy, is a highly effective screening tool. Dr. Perry Pickhardt, MD, emphasizes its excellent performance in detecting flat lesions, a capability that has been demonstrated repeatedly. He notes that oral contrast given during the procedure coats the surface of polyps, acting as a "beacon for detection." Dr. Pickhardt concludes that CT colonography and optical colonoscopy are likely complementary, with virtual colonoscopy possibly having a "slight advantage in some cases" for identifying certain flat polyps.

Screening Guidelines and Importance

Regular screening is the most effective method for preventing colorectal cancer deaths. Dr. Anton Titov, MD, discusses how tests like CT colonoscopy look for important polyps in the large bowel. Current colon cancer screening guidelines recommend initiation at age 50, with repeat exams every 5 to 10 years depending on the modality and findings. Weighing the options is important, but Dr. Perry Pickhardt, MD, underscores that completing regular screening is non-negotiable for early cancer detection and prevention.

Full Transcript

Polyps in the large bowel grow for many years before they become cancer.

How big can a polyp grow before it becomes colon cancer? Is it important to remove all polyps found during colonoscopy? How can CT colonography identify important polyps in the large bowel?

A leading virtual colonoscopy screening expert discusses CT colonography.

Screening for colon cancer is the best method to prevent deaths from colorectal cancer. Screening by virtual colonoscopy looks for polyps in the large bowel.

How does the size of the polyp matter for colorectal cancer screening? What is the significance of different types of polyps for colon cancer diagnosis? Specifically, what is a flat lesion adenoma?

Dr. Perry Pickhardt, MD: It turns out size is actually everything in terms of polyp importance. We call smaller colon polyps, 5 millimeters and less, "diminutive lesions". They do not have any clinical significance. They have almost zero chance of being cancer.

They are far too common in the population to be aggressively removed.

Because the cost and complications from smaller polyp removal will skyrocket. It would be as if you were to remove every mole from everyone's skin. It is just an impractical approach.

Large polyps, 10 millimeters and larger, are important. The vast majority of these advanced adenomas have large size.

Larger polyps are clearly the target for screening and prevention.

That leaves the gray zone of 6 to 9 millimeter size polyps.

Dr. Anton Titov, MD: There is some controversy. Should we aggressively pursue these benign polyps?

Dr. Perry Pickhardt, MD: 6 to 9 mm polyps are a little more common than large polyps. But they are not nearly as common as the tiny diminutive polyps. There is some controversy there.

In our practice, we advise that all large bowel polyps 6 millimeters and greater are to be removed by colonoscopy. But most patients actually choose to follow those polyps at three-year intervals. They wait for the rare case where such polyps grow to one centimeter or greater.

Flat polyps, flat adenomas, is a very important subtopic.

Dr. Anton Titov, MD: It has gained a lot of attention. It is a little confusing, but flat polyps are difficult to detect relative to the obvious pedunculated or sessile polyps. These polyps protrude well into the lumen of the large bowel.

That has always been a consideration: how to identify flat polyps better.

Dr. Perry Pickhardt, MD: But fortunately, flat adenomas are much less aggressive on average. Flat adenomas grow very slowly. We have a lot of time to detect flat adenomas in the large bowel at follow-up of patients.

With care and good technique, both regular optical colonoscopy and CT colonography can detect flat polyps and flat adenomas fairly well. Although flat adenomas will be less conspicuous.

We have seen repeatedly that flat lesion detection rate by virtual colonoscopy has been excellent and similar to optical colonoscopy.

We have a scientific article now that will be published soon. It is looking at serrated polyps in the right colon with CT colonography detection. We show that virtual colonoscopy has very good success for detection of serrated polyps.

We now recognize serrated adenomas as a second pathway to colon cancer. Maybe 10 or 15% of colon cancers are arising from these right-sided "serrated lesions". Serrated adenomas tend to be flat lesions.

The good news is we can detect these serrated lesions with CT colonography with very good accuracy.

Dr. Anton Titov, MD: It is a confusing topic. Because some people have jumped to the conclusion that flat adenomas are more aggressive. But actually, the opposite is true.

Dr. Perry Pickhardt, MD: We take flat adenomas very seriously. But we know that time is on our side with these flat lesions, in general.

CT colonography is able to detect flat polyps as well, if not better, than traditional optical colonoscopy.

Dr. Anton Titov, MD: Yes, it is interesting. Virtual and optical colonoscopies are probably complementary. But it appears that optical and virtual colonoscopies are comparable. CT colonography maybe has a slight advantage in some cases.

There are other cases I have seen where optical colonoscopy might detect a lesion that was difficult to detect by CT colonography. They probably are complementary.

Dr. Perry Pickhardt, MD: We haven't fully worked it out. But because of the oral contrast we give to patients who undergo virtual colonoscopy, it coats these polyps and coats the surface of the flat lesions. It serves as a beacon for detection at CT colonography.

Dr. Anton Titov, MD: It is actually a very useful method for us to detect flat lesions in the bowel.

How often do you need to be screened for colorectal cancer? CT colonography or virtual colonoscopy is one of the best tests to find early colon cancer in time for cure.

Colon Cancer Screening Guidelines recommend screening every 5 to 10 years after 50 years of age. Colon cancer screening: weighing the options is important. But regular screening must be done.

Precancerous colon polyps, flat adenoma polyp: how big can a colon polyp grow before becoming a cancer threat? What is a "flat adenoma"?

Virtual colonoscopy (CT colonography) can detect more rare large bowel and rectal lesions. Flat adenoma and serrated adenoma are two precancerous lesions in the large bowel.

Smaller than 5 millimeter polyps have basically zero chance of being colorectal cancer. Virtual colonoscopy is very good at detecting those polyps that have a chance to be early colorectal cancer or precancerous lesions.

Large polyps, 10 millimeters or one centimeter and larger, are important in screening for colorectal cancer. 6 to 9 mm polyps are in a gray zone for colon cancer risk. 6 to 9 mm polyps are more common than large polyps.

Both regular optical colonoscopy and CT colonography can detect flat polyps (flat adenomas) fairly well.