Ninety percent of cases occur after age 50, with males somewhat more likely to develop polyps than females; therefore, colon cancer screening is usually recommended starting at age 50 for both sexes. It takes approximately 10 years for a small polyp to develop into cancer.
Not every sessile polyp will become cancerous. Only a small minority of all polyps become cancerous. That includes sessile polyps. However, sessile polyps are a greater cancer risk because they're tricky to find and may be overlooked for years.
Colon cancer, or cancer that begins in the lower part of the digestive tract, usually forms from a collection of benign (noncancerous) cells called an adenomatous polyp. Most of these polyps will not become malignant (cancerous), but some can slowly turn into cancer over the course of about 10-15 years.
If polyps are cancerous or have the potential to become so, the doctor is likely to recommend removing them. If the polyps are in an accessible position, the doctor may be able to extract them at the time of the colonoscopy using a procedure called a polypectomy.
Adenomas: Many colon polyps are the precancerous type, called adenomas. It can take seven to 10 or more years for an adenoma to evolve into cancer—if it ever does. Overall, only 5% of adenomas progress to cancer, but your individual risk is hard to predict.
The risk of polyps smaller than 5 millimeters (mm) being cancerous is very low. In larger polyps, the risk of cancer increases. Colon polyps grow very slowly and often do not cause symptoms. Regular colon cancer screenings can help detect them before they become cancerous.
The growth and mutation of colon polyps into cancer is a slow process, taking an estimated 10 years on average. So as long as patients are screened, it is unlikely they will develop cancerous polyps.
Polyps grow in two different shapes: flat (sessile) and with a stalk (pedunculated). Sessile polyps are more common than previously thought and harder to detect in colon cancer screening. They lie flat against the surface of the colon's lining, also known as the mucous membrane.
Cancerous and Precancerous Polyps
Both pedunculated and sessile polyps can turn into benign (non-cancerous), precancerous and cancerous polyps. It's important to know your polyp type – such as hyperplastic, inflammatory, hamartomatous, adenomatous, hyperplastic and sessile serrated – to know your cancer risk.
It does not have a stalk, like a pedunculated polyp, making it harder to find and remove. A certain type of sessile polyp, called sessile serrated adenoma, is considered precancerous and may be a precursor for up to 30% of all colorectal cancers.
Approximately 6% of colorectal cancers are diagnosed within 3 to 5 years after the patient received a colonoscopy, according to findings from a recent population-based study.
This means cancer and polyps can sometimes go undetected. So, despite having had a 'clear' colonoscopy, some patients go onto develop bowel cancer – referred to as post-colonoscopy colorectal cancer (PCCRC) or 'undetected cancer'.
Polyp Growth Rates
Cancerous polyps tend to grow slowly. It is estimated that the polyp dwell time, the time needed for a small adenoma to transform into a cancer, may be on average 10 years (17). Evidence from the heyday of barium enema examinations indicates that most polyps do not grow or grow very slowly (18).
Although these two types have some distinctive features on gross appearance, they cannot be reliably distinguished endoscopically. Left panel: a typical small sessile hyperplastic polyp that is less than 5 mm in size.
The task force recommends patients who have had 3 to 4 sessile serrated polyps <10 mm removed during baseline colonoscopy to repeat screening in 3 to 5 years; patients who have had 5 to 10 sessile serrated polyps <10 mm removed at a high-quality examination should schedule a repeat colonoscopy within 3 years.
Polypectomy Techniques
It has been recommended that all sessile polyps larger than 3 mm be removed with a cold or hot snare with a rim of normal surrounding tissue rather than with biopsy forceps to allow complete removal [3].
Polyps are common in American adults, and while many colon polyps are harmless, over time, some polyps could develop into colon cancer. While the majority of colon cancers start as polyps, only 5-10% of all polyps will become cancerous.
How long does it take a polyp to turn into a cancer? Generally, it's about a 10- to 15-year process, which explains why getting a colonoscopy screening once every 10 years is sufficient for most people. However, this chain of events may occur faster in people with hereditary colorectal cancer syndromes.
What are flat polyps? Polyps are lesions found in the colon that are removed during colonoscopy. Many of them would never cause a serious health problem, but some are adenomas — precancerous growths that could turn cancerous over time.
The average change in diameter for SSA/Ps was 1.5 mm, corresponding to 0.3 mm/year of growth, which was the same for TAs (0.3 mm/year, p=0.922).
Most colorectal cancers start as a growth on the inner lining of the colon or rectum. These growths are called polyps. Some types of polyps can change into cancer over time (usually many years), but not all polyps become cancer. The chance of a polyp turning into cancer depends on the type of polyp it is.
The smaller the polyp, the less likely it is to be on the road to cancer, says Dr. Gunter. Polyps can range in size from the less-than-5-millimeter “diminutive” category to the over-30-millimeter “giants.”
Most polyps are benign (not cancerous). Your doctor can tell if a colon polyp is cancerous during a colonoscopy by collecting tissue to biopsy. The results of the biopsy are typically sent to your doctor within a week. Only 5% to 10% of all polyps become cancerous.
ANSWER: It is rare for uterine polyps to be cancerous. If they aren't causing problems, monitoring the polyps over time is a reasonable approach. If you develop symptoms, such as abnormal bleeding, however, then the polyps should be removed and evaluated to confirm that there is no evidence of cancer.
Approximately 1% of polyps with a diameter less than 1 centimeter (cm) are cancerous. More than one polyp or a polyp that is 1 cm or bigger places you at higher risk for colon cancer. Up to 50% of polyps greater than 2 cm (about the diameter of a nickel) are cancerous.