From the Guidelines
Colonic adenomas have a significant risk of progressing to colorectal cancer, with the risk varying based on several factors, including size, histology, and number of polyps. The risk of colonic adenomas becoming cancerous is a significant concern, with most colorectal cancers developing from adenomatous polyps.
- The transformation from adenoma to cancer typically takes 7-10 years, providing an opportunity for intervention through screening and removal 1.
- Larger polyps (>1 cm) have a higher risk of malignant transformation, with a reported rate of 7.3% for polyps measuring 10-20 mm 1.
- The risk also increases with certain characteristics, such as villous histology, high-grade dysplasia, and multiple polyps.
- Age is another factor, with older patients facing greater risk.
- After adenoma removal, follow-up colonoscopies are essential, typically recommended at 3-5 year intervals depending on the number, size, and histology of the polyps found.
- This surveillance schedule allows for detection and removal of new or recurrent adenomas before they progress to cancer, significantly reducing colorectal cancer risk. Some key factors to consider when assessing the risk of colonic adenomas include:
- Size: larger polyps have a higher risk of malignant transformation
- Histology: villous adenomas carry higher risk than tubular adenomas
- Number: multiple polyps indicate higher risk
- Age: older patients face greater risk
- Family history: patients with a family history of colorectal cancer are at higher risk The most recent and highest quality study, published in 2018, provides the most up-to-date guidance on the risk of colonic adenomas becoming cancerous, and should be used to inform clinical decision-making 1.
From the Research
Risk of Colonic Adenomas Becoming Cancer
The risk of colonic adenomas becoming cancer is a significant concern, and several studies have investigated this topic.
- A study published in Gastroenterology in 2020 found that individuals with advanced adenomas had a higher risk of colorectal cancer (CRC) compared to those with non-advanced adenomas or no polyps 2.
- Another study published in Digestive diseases and sciences in 2022 found that solid organ transplantation recipients were at a higher risk of developing advanced colonic adenomas, suggesting that earlier surveillance should be considered 3.
- A population-based case-control study published in the Journal of clinical oncology in 2012 found that the risk of CRC was significantly reduced within 5 years after polypectomy, particularly for left-sided CRC 4.
- A retrospective cohort study published in Surgical endoscopy in 2022 found that the prevalence of subsequent adenomas, especially high-risk adenomas, during surveillance was not well known, and that guideline adherence was low 5.
- A comprehensive evaluation of risk factors and surveillance use published in Gut in 2024 found that patients with high-risk polyps were at a higher risk of subsequent CRC and high-risk polyps, and may benefit from early surveillance within 3 years 6.
Factors Influencing the Risk of Colonic Adenomas Becoming Cancer
Several factors can influence the risk of colonic adenomas becoming cancer, including:
- The type and size of the adenoma: Advanced adenomas (≥10 mm, high-grade dysplasia, or tubulovillous or villous histology) are at a higher risk of becoming cancerous 2, 3.
- The presence of serrated polyps: Serrated polyps, particularly large ones (≥10 mm), are at a higher risk of becoming cancerous 2, 6.
- The timing of surveillance colonoscopy: Earlier surveillance within 3 years may be beneficial for patients with high-risk polyps 4, 6.
- The use of surveillance colonoscopy: Surveillance colonoscopy is associated with a lower risk of CRC, particularly among patients with high-risk polyps 5, 6.