Sessile polyps are growths that form on the inner lining of an organ, most commonly the colon. They are characterized by their flat, broad-based attachment, distinguishing them from polyps that grow on a stalk. While many sessile polyps are non-cancerous, some possess the potential to develop into cancer over time. This article explains how the size of these polyps relates to their cancer risk, along with other important contributing factors and subsequent management strategies.
Understanding Sessile Polyps
Sessile polyps are typically detected during a colonoscopy, a procedure where a doctor uses a flexible tube with a camera to view the lining of the large intestine. Unlike pedunculated polyps, which resemble mushrooms on a stalk, sessile polyps lie flat against the tissue, making them sometimes more challenging to identify.
Polyps are common, especially in adults over 45, affecting about 20% of adults overall and 40% of those over 50. Most polyps are benign, meaning they are not cancerous. However, some types, particularly adenomatous polyps, can become cancerous if left unaddressed.
How Size Affects Cancer Risk
The size of a sessile polyp significantly indicates its potential for malignancy. Larger sessile polyps are associated with a higher risk. For instance, polyps smaller than 5 millimeters (mm) have a very low likelihood of being cancerous, with some studies reporting 0% incidence.
As polyps grow, the risk increases. Polyps measuring between 5-9 mm still have a relatively low risk, but this risk rises notably for those 10 mm (1 cm) or larger. Approximately 30-50% of polyps larger than 2 cm may be cancerous. This correlation exists because larger polyps have had more time for abnormal cell growth and a greater surface area where cellular changes can occur, potentially leading to cancerous transformation.
Other Factors Influencing Risk
Beyond size, other characteristics and patient-specific factors influence the likelihood of a sessile polyp being or becoming cancerous. The histology, or the type of cells observed under a microscope, is a primary determinant of risk. Adenomatous polyps, which include tubular, villous, and tubulovillous types, are considered precancerous. Villous adenomas, characterized by their sprawling, fern-like appearance, carry a higher cancer risk compared to tubular adenomas.
Sessile serrated polyps (SSPs), also known as sessile serrated lesions (SSLs), are a distinct type of sessile polyp with a saw-tooth appearance under the microscope. These polyps are significant precursors to colorectal cancer, accounting for 20-30% of all colorectal cancers. While hyperplastic polyps, another serrated type, are typically non-malignant, larger or proximally located hyperplastic polyps may have malignant potential. The number of polyps found also impacts risk; having multiple polyps, particularly more than three, increases risk.
A patient’s personal and family medical history also influences risk. Individuals with a history of inflammatory bowel disease (IBD), such as ulcerative colitis or Crohn’s disease, have increased risk of colorectal polyps and cancer. Genetic syndromes like Familial Adenomatous Polyposis (FAP) or Lynch syndrome significantly elevate polyp and cancer risk, often requiring earlier, more frequent screenings. The pathologist’s report, detailing the polyp’s type and cellular features, is essential for comprehensive risk assessment.
Management and Follow-Up
Once sessile polyps are detected during a colonoscopy, they are typically removed during the same procedure through a process called polypectomy. This prevents them from developing into colorectal cancer. For larger or more complex polyps, specialized techniques like endoscopic mucosal resection (EMR) may be employed, sometimes removed in pieces.
After polyp removal, regular surveillance colonoscopies are recommended, with the interval determined by the polyp’s size, number, and pathology:
- One or two small adenomas: 7 to 10 years.
- Three to four adenomas: 3 to 5 years.
- High-risk findings (e.g., five to ten adenomas, adenomas >10 mm, sessile serrated polyps with dysplasia): 3 years.
- More than ten adenomas: Less than one year.
Lifestyle factors, including a healthy diet and regular exercise, can also contribute to reducing the risk of polyp formation and recurrence.