the global prevalence of colorectal cancer is increasing , and the incidence in south korea is rapidly increasing owing to a westernized diet .
colon carcinogenesis occurs through either the adenoma - carcinoma sequence or a de novo pathway .
it is known that over two - thirds of colorectal cancer cases develop from adenomas ; therefore , detection and removal of adenomas by colonoscopy is the best way to prevent colorectal cancer . according to an american study in 2008 ,
polyps over 9 mm in size have been detected in 6% to 7% of health screening examinations ; the reported adenoma detection rate in korea varies , but is approximately 9% during screening examinations . diagnosis and removal of colorectal polyps is increasing because of the widespread availability of colonoscopy .
follow - up colonoscopy is required to reduce the risk of colorectal carcinogenesis after polypectomy for adenoma .
metachronous lesions were detected in 20% to 30% of patients during follow - up colonoscopy 3 to 5 years after polypectomy to remove one or more adenomas [ 3 - 7 ] .
advanced adenomas ( > 10 mm in diameter , over 25% villous component , or high - grade dysplasia ) were found in 20% of these patients [ 3 - 8 ] , and a small number had invasive colorectal cancer [ 5,9 - 14 ] .
in addition , interval cancer was reported during an adequate follow - up period after screening colonoscopy [ 15 - 17 ] , and 19% to 27% of such interval cancers are known to be caused by incomplete removal of polyps .
enhanced colonoscopy surveillance may be needed for screening of patients at high risk of colorectal carcinogenesis , for prediction of progressive colorectal tumor development , management of incompletely removed polyps , and appropriate follow - up .
follow - up colonoscopy is required because the risk of colorectal cancer after polypectomy is higher than that in patients without polyps . an appropriate interval for follow - up colonoscopy
was recommended in korea in 2012 , based on features of polyps detected by colonoscopy and the risk of progression to an advanced neoplasm during this interval .
it is known that number , size , and histological characteristics of adenomas should be considered in postpolypectomy surveillance .
the probability of detecting an advanced adenoma or tumor is increased when the number of adenoma is 3 or more . according to previous studies that evaluated the correlation between risk of advanced neoplasm and the number of adenomas found during follow - up [ 21 - 29 ]
, the risk increases with the number of adenomas : combined odds ratio ( or ) 1.93 ( 95% confidence interval [ ci ] , 1.51 to 2.45 ) and combined hazard ratio ( hr ) 2.20 ( 95% ci , 1.49 to 2.90 ) .
the risk of neoplasm development is especially increased in patients with three or more adenomas : combined or 2.84 ( 95% ci , 1.26 to 6.39 ) and combined hr 2.20 ( 95% ci , 1.40 - 3.46 ) .
thus , established international guidelines recommend follow - up in 3 years in patients with three or more adenomas .
the british society of gastroenterology - association of coloproctology of great britain and ireland guidelines define cases with five or more adenomas , or three or more adenomas including an adenoma over 1 cm in size , as high - risk , and recommend follow - up after 1 year .
the us multi - society task force on colorectal cancer - american cancer society guidelines recommend follow - up in 3 years , and consideration of familial polyposis in cases with 10 or more adenomas .
moreover , several guidelines recommend follow - up after 1 year for cases with five or more adenomas or with three or more polyps including adenomas over 1 cm in size . in cases with detection and removal of 10 or more polyps ,
diminutive polyps are < 5 mm in size , small polyps are between 6 and 9 mm , and large polyps are larger than 10 mm . according to studies evaluating the risk of development of an advanced neoplasm based on the size of a preexisting adenoma [ 21 - 25,27 - 29 ] ,
the risk is not significantly increased for adenomas between 5 and 10 mm in comparison with the risk for those under 5 mm .
however , the risk of development of an advanced neoplasm is increased for adenomas over 10 mm in size , with a rate two times higher than in cases with adenomas under 10 mm .
larger adenomas include more villous components and are more likely to show advanced pathology ; therefore , a maximum 32% of polyp over 20 mm are reported to include malignant portions .
it is important to assess pathologic completeness when larger sessile polyps are removed , but sessile polyps over 20 mm are difficult to remove with conventional snare polypectomy , and most are removed by piecemeal resection .
follow - up after 1 year is not mandatory for polyps between 1 and 2 cm in size , but should be performed in 1 year in the case of incomplete removal .
determination of completeness is important for sessile polyps over 2 cm in size , and follow - up study after 6 to 12 months is required if completeness is not confirmed .
however , cases with over 20% to 25% villous components in a preexisting adenoma are defined as tubulovillous or villous adenomas ; several studies have reported that the risk of development of an advanced neoplasm is significantly increased in patients with tubulovillous or villous adenomas , compared with patients with tubular adenoma alone : combined or 1.51 ( 95% ci , 1.16 to 1.97 ) and combined hr 1.83 ( 95% ci , 1.15 to 2.89 ) .
a korean study reported that the risk of development of an advanced adenoma is not increased for the villous adenoma component in a preexisting adenoma ( hr , 1.48 ; 95% ci , 0.74 to 2.95 ) .
however , yang et al .   reported that the risk of development of an advanced adenoma is significantly increased with tubulovillous or villous pathology ( or , 8.1 ; 95% ci , 4.2 to 15.6 ) , in a 16-year follow - up study after adenoma removal by sigmoidoscopy , and suggested that tubulovillous or villous pathology is the most important predictive factor for risk of advanced neoplasm after polypectomy , along with high - grade dysplasia .
an increasing trend for the risk of advanced neoplasm was observed in cases with high - grade dysplasia detected by colonoscopy , compared to cases with low - grade dysplasia : combined or 1.33 ( 95% ci , 0.85 to 2.09 ) and combined hr 1.69 ( 95% ci , 1.14 to 2.50 ) .
stage adjustment at follow - up is required for such cases , but martnez et al .  
reported that the risk is not high . a meta - analysis by saini et al .  
recommends follow - up after 3 years , because high - grade dysplasia and the number of adenomas are the most meaningful factors in the prediction of increased risk for advanced adenoma : combined relative risk 1.84 ( 95% ci , 0.53 to 8.93 ) .
it was recently reported that serrated polyps progress to colorectal cancer through a pathway different from the adenoma - carcinoma sequence .
sessile serrated adenomas include hyperplastic polyps , traditional serrated adenomas , and mixed adenomatous and hyperplastic polyps , which have serrated pathological architecture .
serrated polyps mostly occur in the right colon , and most are associated with braf and/or msi - high mutations , and are predicted to rapidly progress to colorectal cancer .
the combined or in serrated polyp cases at risk for development of advanced neoplasm was 1.98 ( 95% ci , 1.24 to 3.15 ) ; moreover , the presence of a serrated polyp over 10 mm in size reportedly increases the risk of development of an advanced neoplasm .
the risk of a progressive neoplasm has a combined or of 1.73 ( 95% ci , 1.48 to 2.01 ) when the adenoma is found in the right colon , defined as the colon from cecum to transverse colon or splenic flexure , compared to adenoma located in the left colon .
further investigation is required to determine whether an adenoma in the right colon is a risk factor for advanced neoplasm because colonoscopy may miss a tumor owing to the anatomical characteristics of the right colon , which has sharp curves and distinct haustra ; moreover , cancer in the right colon can be caused by the serrated pathway and can be affected by individual patient features and environmental factors .
the korean 2012 guidelines recommend surveillance 5 years after polypectomy for groups that are not at a high risk for advanced neoplasm development ; less frequent follow - up is recommended for cases with previous colonoscopy findings related to an increased risk , even if the findings of current colonoscopy suggest no increased risk .
follow - up colonoscopy 3 years after polypectomy is recommended for cases with a high risk of carcinogenesis .
however , the follow - up interval should be reduced when well - known conditions are not satisfied , or based on previous colonoscopy findings , completeness of removal , health status , family history , and past medical history ( table 1 ) .
the prevalence of colorectal cancer is increasing , and adequate postoperative surveillance is required for patients who undergo polypectomy during colonoscopy , because of higher risk for development of an advanced neoplasm .
an increased risk of subsequent neoplasia occurs because of polypectomy of three or more adenomas , any adenomas larger than 10 mm , any tubulovillous or villous adenoma , any adenoma with high - grade dysplasia , or any serrated polyp larger than 10 mm ( table 2 ) .
patients with any of these findings are defined as a high - risk group , and colonoscopy 3 years after complete removal is recommended . in addition , the surveillance period can be reduced based on previous colonoscopy findings , completeness of removal , health status , family history , and past medical history ; follow - up colonoscopy at 5 years after polypectomy is recommended for low- or intermediate - risk patients .
recommendations from other countries can not be applied because the korean reimbursement system is based on cost - effectiveness .
therefore , management of polyps requires further cost - effectiveness analysis relevant to health care in korea .
 the detection and removal of adenomatous polyps and postpolypectomy surveillance are considered important for the control of colorectal cancer ( crc ) . 
 surveillance using colonoscopy is an effective tool for preventing crc after colorectal polypectomy , especially if compliance is good . in current practice , 
 the intervals between colonoscopies after polypectomy are variable . 
 different recommendations for recognizing at risk groups and defining surveillance intervals after an initial finding of colorectal adenomas have been published . 
 however , high - grade dysplasia and the number and size of adenomas are known major cancer predictors . based on this , a subgroup of patients that may benefit from intensive surveillance colonoscopy can be identified . 
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