COLON CANCER SCREENING - INCREASED RISK
Adenoma Characteristics
Size - Adenoma size is the most important predictor of cancer risk. The size of an adenoma is based on its diameter.

  • Adenoma ≥ 10 mm in diameter - adenomas that are ≥ 10 mm in diameter are associated with an increased risk of cancer regardless of their histological properties. In a study that looked at the histology of 949 polyps ≥ 10 mm in size, 2.6% were cancerous and 27.6% were advanced adenomas.

  • Adenoma 6 - 9 mm in diameter - adenomas that are 6 - 9 mm in size are mostly benign and the benefits of removing these lesions is controversial. In a study that looked at the histology of 1198 polyps 6 - 9 mm in size, 0.2% were cancerous and 6.5% were advanced adenomas. Polyps in this size range can also regress. A study that followed the natural course of polyps 6 - 9 mm in size with CT colonography over an average of 2.3 years found the following:
    • 22% progressed in size (of these, 91% were advanced adenomas upon removal)
    • 50% remained stable (of these, 4% were advanced adenomas upon removal)
    • 28% regressed in size (of these, 0% were advanced adenomas upon removal)
    • 10% resolved

  • Adenoma ≤ 5 mm in diameter - adenomas that are ≤ 5 mm in diameter are rarely found to be cancerous or advanced adenomas. In a study that looked at the histology of 3744 polyps ≤ 5 mm in size, 1 was found to be cancerous and 1.7% were advanced adenomas. [16,17]
Histology - Histology is the second most important factor in predicting cancer risk. In general, adenomas can be divided into two large groups based on their histology - conventional adenomas and serrated adenomas. Degree of dysplasia is another factor that affects cancer risk in both types of adenomas.

  • Conventional adenomas - conventional adenomas are divided into 2 subgroups: tubular and villous/tubulovillous
    • Tubular adenomas - tubular adenomas are the most common type of adenoma accounting for just over half of all polyps. Tubular histology is considered low risk for cancer. People with ≥ 3 tubular adenomas are at increased risk of cancer.
    • Villous and tubulovillous adenomas - villous and tubulovillous histologies are uncommon in adenomas < 10 mm in size (< 10%). They are present in about 22% of adenomas ≥ 10 mm in size. Villous/tubulovillous histology is associated with an increased risk of cancer.

  • Serrated adenomas - serrated adenomas are divided into 3 subgroups - hyperplastic polyps, sessile serrated adenoma/polyp, and traditional serrated adenoma. Small hyperplastic polyps are quite common accounting for up to 41% of polyps ≤ 5 mm found on screening colonoscopy. Sessile serrated adenomas/polyps are much less common making up about 2% of all polyps. Traditional serrated adenomas are very rare. Patients with multiple serrated polyps should be evaluated for serrated polyposis syndrome.
    • Hyperplastic polyps - hyperplastic polyps are almost always sessile or flat. They are very common and not considered precancerous.
    • Sessile serrated adenoma/polyp - sessile serrated adenomas/polyps are flat and precancerous.
    • Traditional serrated adenoma - traditional serrated adenomas are typically flat but may also be pedunculated. They are rare and precancerous. [13,16,17]
Location
  • Adenomas that are located more proximally (closer to the right side or ascending colon) have been shown in some studies to convey a higher risk of cancer. Other studies have not found an increased risk.
  • Current surveillance guidelines do not make recommendations based on polyp location [14]


  • Average age of patients was 68.6 years and 44.6% were male
  • Reference [15]
Prevalence of CRC and Polyps in 4404 Patients at Average Risk for CRC who had a Screening Colonoscopy
Finding Prevalence
CRC 0.7%
Advanced adenoma 9.7%
Tubular adenomas < 10 mm or hyperplastic polyps 37%
No polyp 52.6%


  • Average age of subjects (N=122,899) at initial endoscopy was 58 years.
  • Most subjects in the study had > 2 surveillance colonoscopies over a median follow-up of 10 years
  • Reference [18]
CRC Risk Based on Findings from Initial Colonoscopy/Flex sig
Finding 5-year CRC Risk 10-year CRC Risk
Advanced adenoma 0.6% 1.7%
Nonadvanced adenoma 0.1% 0.3%
Serrated polyp ≥ 10 mm 0.4% 1.1%
Serrated polyp < 10 mm 0.1% 0.4%
No polyp 0.2% 0.4%


  • Reference [19]
ACG 2021 Screening Recommendations Based on Family History
One first-degree relative with CRC or advanced polyp at age < 60 years, or ≥ 2 first-degree relatives with CRC or advanced polyp at any age
  • Initial screening age: 40 years, or 10 years before the age of diagnosis of the youngest affected first-degree relative, whichever is earlier
  • Screening method and interval: Colonoscopy every 5 years
One first-degree relative with CRC or advanced polyp at age ≥ 60 years
  • Initial screening age: 40 years, or 10 years before the age of diagnosis of the youngest affected first-degree relative
  • Screening method and interval: Perform initial colonoscopy, then follow average-risk recommendations
One second-degree relative with CRC or advanced polyp
  • Follow average-risk screening recommendations

  • Reference [11]
AGA 2018 Screening Recommendations Based on Family History
One first-degree relative with CRC
  • Initial screening age: 40 - 50 years, or 10 years younger than the age of diagnosis of the first-degree relative, whichever is earlier
  • Screening method: Colonoscopy (preferred) | FIT (second-line)
  • Screening interval:
    • Colonoscopy: every 5 - 10 years
    • FIT: every 1 - 2 years
≥ 2 first-degree relatives with CRC
  • Initial screening age: 40 years, or 10 years younger than the age of diagnosis of the earliest diagnosed first-degree relative, whichever is earlier
  • Screening method: Colonoscopy
  • Screening interval: every 5 years
≥ 1 second-degree relative with CRC
  • Initial screening age: 50 years
  • Screening method: same as average-risk
  • Screening interval: same as average-risk
≥ 1 first-degree relative with advanced adenoma
  • Initial screening age: 40 - 50 years or 10 years younger than the age of diagnosis of the earliest diagnosed first-degree relative, whichever is earlier
  • Screening method: Colonoscopy or FIT
  • Screening interval:
    • Colonoscopy: every 5 - 10 years
    • FIT: every 1 - 2 years
≥ 1 first-degree relative with non-advanced adenoma or polyp of unknown histology
  • Initial screening age: same as average-risk
  • Screening method: same as average-risk
  • Screening interval: same as average-risk

  • Reference [9,10]
USMSTF 2017 Screening Recommendations Based on Family History
Single first-degree relative with CRC or advanced adenoma diagnosed at age < 60 years or two first-degree relatives with CRC or advanced adenomas diagnosed at any age
  • Initial screening age: begin 10 years before the age at diagnosis of the youngest affected relative or age 40, whichever is earlier
  • Screening method: Colonoscopy
  • Screening interval: Every 5 years
Single first-degree relative with CRC or advanced adenoma diagnosed at age ≥ 60 years✝
  • Initial screening age: 40 years
  • Screening methods: Same as average-risk patients (e.g colonoscopy, FIT, etc.)
  • Screening interval: Follow same recommendations as average-risk patients
✝ The ACS recommendations say that patients with two second-degree relatives who meet this criteria at any age should also be included in this recommendation






  • All recommendations are for people who were at average risk before their screening colonoscopy
  • See continued surveillance for recommendations on subsequent colonoscopy intervals
  • Reference [14]
USMSTF Recommendations for Post-colonoscopy Follow-up of Conventional Adenomas
Screening colonoscopy finding Interval before first follow-up colonoscopy
  • 1 - 2 tubular adenomas < 10 mm in size
 7 - 10 years
  • 3 - 4 tubular adenomas < 10 mm in size
 3 - 5 years
  • 5 - 10 tubular adenomas < 10 mm in size
 3 years
  • Adenoma ≥ 10 mm in size
 3 years
  • Adenoma with tubulovillous or villous histology
 3 years
  • Adenoma with high-grade dysplasia
 3 years
  • > 10 adenomas on a single exam
 1 year
  • Piecemeal resection of adenoma ≥ 20 mm
 6 months

  • See polyp types for a review of the different types of serrated polyps
  • All recommendations are for people who were at average risk before their screening colonoscopy
  • See continued surveillance for recommendations on subsequent colonoscopy intervals
  • Patients with multiple serrated polyps should be evaluated for serrated polyposis syndrome
  • Reference [14]
USMSTF Recommendations for Post-colonoscopy Follow-up of Serrated Polyps
Screening colonoscopy finding Interval before first follow-up colonoscopy
  • ≤ 20 hyperplastic polyps in rectum or sigmoid colon < 10 mm in size
 10 years
  • ≤ 20 hyperplastic polyps proximal to sigmoid colon < 10 mm in size
 10 years
  • 1 - 2 sessile serrated polyp(s) < 10 mm in size
 5 - 10 years
  • 3 - 4 sessile serrated polyps < 10 mm in size
 3 - 5 years
  • 5 - 10 sessile serrated polyps < 10 mm in size
 3 years
  • Sessile serrated polyp ≥ 10 mm
 3 years
  • Sessile serrated polyp with dysplasia
 3 years
  • Hyperplastic polyp ≥ 10 mm
 3 - 5 years
  • Traditional serrated adenoma
 3 years
  • Piecemeal resection of sessile serrated polyp ≥ 20 mm
 6 months



  • Reference [14]
1 - 4 tubular adenomas < 10 mm found on initial colonoscopy
Findings on first follow-up colonoscopy Recommended interval for next surveillance
Normal 10 years
1 - 2 tubular adenomas < 10 mm 7 - 10 years
3 - 4 tubular adenomas < 10 mm 3 - 5 years
High-risk adenoma 3 years

  • Reference [14]
High-risk adenoma found on initial colonoscopy
Findings on first follow-up colonoscopy Recommended interval for next surveillance
Normal 5 years
1 - 2 tubular adenomas < 10 mm 5 years
3 - 4 tubular adenomas < 10 mm 3 - 5 years
High-risk adenoma 3 years