colorectal cancer is the third most common incident cancer among men and the second most common cancer among women worldwide . incidence rates vary 10-fold in both sexes worldwide , and the highest rates are estimated in more developed regions , such as north america and western europe , whereas the lowest rates are estimated in africa ( except southern africa ) and south - central asia . in asia , colorectal cancer is the fourth most common incident cancer among men and the fifth most common cancer among women . although incidence rates are relatively low in asian countries , those for east asian countries are relatively high . in korea , annual percentage changes in age - standardized incidence rates were 6.2% in men and 6.8% in women between 1999 and 2009 using the world standard population as a standard population . in 2009 , 24,986 new colorectal cancer cases ( 15,068 men and 9,918 women ) were diagnosed , accounting for 13.0% of all cancer occurrences . colorectal cancer is the second most common cancer after stomach cancer among men and the third most common cancer after cancers of the thyroid and breast among women . there have been several reports on differences in patterns of colorectal incidence trends according to age group , sex , and anatomical location [ 3 - 5 ] . however , it has not been properly investigated whether colorectal cancers of a specific age group , sex , or anatomical location show more rapid increases in the korean population . the aim of the current study was to demonstrate changing trends of colorectal cancer incidence according to age group , sex , and anatomical location . the korea central cancer registry ( kccr ) , a nation - wide , hospital - based cancer registry , was initiated by the ministry of health and welfare , korea in 1980 . the registry collected information on approximately 80 - 90% of cancer cases from more than 150 training hospitals across the country , and , in 1999 , the kccr expanded cancer registration to cover the entire korean population under the population - based regional cancer registry program . age ( five - year intervals ) and sex - specific incidence rates and the number of cases of colorectal cancer between 1999 and 2009 were obtained from the korea national cancer incidence database . anatomical subsites were defined based on the tenth version of the international statistical classification of diseases and related health problems , 10th revision ( icd-10 ) . we defined the proximal colon as the cecum ( c18.0 ) , appendix ( c18.1 ) , ascending colon ( c18.2 ) , hepatic flexure ( c18.3 ) , transverse colon ( c18.4 ) , and splenic flexure of the colon ( c18.5 ) ; the distal colon was defined as the descending colon ( c18.6 ) and sigmoid colon ( c18.7 ) . overlapping lesions of the colon ( c18.8 ) and colon not otherwise specified ( c18.9 ) were not included in the subsite analysis . age - standardized rates ( asrs ) were calculated using the middle - year population of 2,000 as the standard population . annual percent changes ( apcs ) for the incidence rates were calculated using a linear model , according to the following formula ; ( exp(b)-1)100 , where b is the slope of the regression of the natural logarithm of the asr in a calendar year . the 95% confidence intervals ( cis ) were obtained with a standard error from the fit of the regression and the t - distribution function . all analyses were conducted by sex , subsite , and age group ( 10-year intervals ) . male - to - female incidence rate ratios ( irr ) were calculated using the numbers of cancer patients for each site and the sex - specific population structure for each year using stata / se 10.0 for windows ( stata corp lp , college station , tx ) . statistical significance in difference between irrs the asrs and apcs overall and for each subsite of colorectal cancer by sex are shown in tables 1 and 2 and fig . 1 . among men , the asr for colorectal cancer was 27 per 100,000 in 1999 and increased to 50.2 in 2009 ( apc , 6.6% ) . the asr for colorectal cancer among women was 17.2 in 1999 and 26.9 in 2009 ( apc , 5.1% ) . the rectum was the most common cancer site among both men and women in 1999 and 2009 . cancer of the distal colon showed the highest apc ( 10.8% among men and 8.4% among women ) , followed by the proximal colon ( 7.9% among men and 6.6% among women ) and rectum ( 5.2% among men and 2.4% among women ) . as a result , the proportion of rectal cancer decreased from 51.5% in 1999 to 47.1% in 2009 among men , and from 50.5% in 1999 to 42.8% in 2009 among women , whereas the proportion of proximal and distal colon cancers increased among both men and women ( appendix 2 ) . in all subsites , significantly higher apcs were observed among men , compared with women . as a result , the male - to - female irrs showed a significant increase between 1999 and 2009 for overall colorectal cancer ( 1.20 in 1999 to 1.51 in 2009 ) , distal colon cancer ( 1.32 to 1.60 ) , and rectal cancer ( 1.22 to 1.67 ) , whereas the irr for proximal colon cancer did not show a significant change ( 1.09 to 1.16 ) ( table 3 ) . the asrs and apcs for colorectal cancer subsites by age group are shown in tables 4 and 5 . for overall colorectal cancer , men who were in their 60s showed the highest increase , whereas , for women , those in their 80s showed the highest increase . distal colon cancer consistently showed the highest apc in most age groups among both men and women , except for women in their 80s , who showed the highest apc for proximal colon cancer . among women , for almost every subsite , the most notable increases in incidence were observed for the oldest age group . proximal colon cancer in men also showed the highest apc in the oldest age groups , whereas apcs were significantly higher only in the 60s for distal colon cancer and 40s and 60s for rectal cancer . however , the apcs showed narrow ranges of between 10.1 and 11.7 for distal colon cancer and between 4.7 and 5.8 for rectal cancer among men over 40 years old . the highest male - to - female irrs for overall colorectal cancer were observed for the oldest age groups , whereas the lowest irrs were observed for younger age groups ( table 6 ) . however , significant increases in male - to - female irrs were observed in their 50s and 60s between 1999 and 2009 . in the subsite - specific analyses , the changes in male - to - female irrs between 1999 and 2009 showed a statistically significantly increase for rectal cancer among men and women in their 50s , and 60s and for distal colon cancer among those in their 60s . incidence of colorectal cancer has increased in most countries , except for the united states and some areas of japan . the most significant increases have been observed in eastern european countries and most asian countries . although the korean population has experienced a rapid increase in colorectal cancer incidence , it has not been properly investigated whether the increasing pattern differs according to age group , sex , or anatomical location . there have been suggestions that colorectal cancer incidence by subsite differs according to race , sex , age group , and time period . in our study , rectal cancer accounted for the highest proportion among all subsites and ranged from 41% to 51% of all colorectal cancers . this result is consistent in part with a report from the us , which showed that the rectum ( c19.9 and c20.9 ) was the most common subsite for male asians and pacific islanders living in the us ( 35% ) , whereas the proximal colon was the most common site for whites and blacks among both men and women , as well as female asians and pacific islanders . however , in the current study , the apc for rectal cancer was the lowest among the subsites included , thus , it appears that the proportion of rectal cancer has decreased among both men and women in korea . instead , colon cancer , particularly distal colon cancer , has shown a rapid increase . we expect that the proportion of rectal cancer will continue to decrease in the future , and the proportion will eventually reach a level similar to that of western countries . one study suggested that incidence of colorectal cancer has increased among younger age groups in the us population , although overall incidence of colorectal cancer has declined . the increases observed in the younger population were mainly attributed to rectal cancer . in our study , we did not find clear evidence for a more rapid increase in overall incidence of colorectal cancer or rectal cancer in younger age groups , compared to older age groups in women . in men , however , it is worthy of mention that , unlike proximal colon cancer and distal colon cancer , where the apcs were lowest in their 30s and 40s , the apcs of rectal cancer in men in their 30s and 40s were statistically higher than those for men in their 70s and 80s . it is notable that although the incidence was higher among men than among women , the apcs were also higher among men than among women for most subsites . as a result , the male - to - female irr for overall colorectal cancer increased from 1.20 in 1999 to 1.51 in 2009 . a high male - to - female irr was observed for most subsites across ethnic groups in the us population . our study also showed that the lowest male - to - female irr was observed for proximal colon cancer , indicating that the proportion of proximal colon cancer was higher among women than men . this result is consistent with results reported from the us , germany , and japan . traditionally , differences in the distribution of colorectal cancer subsites between men and women have been explained by the role of female hormonal factors . rapid increases in colorectal cancer incidence and the stabilization of colorectal cancer mortality in the korean population could be explained by introduction of colorectal cancer screening . colorectal cancer screening programs were introduced in 2004 as a part of the national cancer screening program for medical aid recipients and national health insurance beneficiaries in the lower income bracket . the fecal occult blood test ( fobt ) is provided free of charge as a primary modality for men and women aged 50 years or older . fobt - positive individuals were provided follow - up by either colonoscopy or double - contrast barium enema . the participation rate was only 10.5% in 2004 , however , it increased to 21.1% in 2008 . according to the korea national cancer screening survey , which covers organized and opportunistic cancer screening programs , lifetime screening rates for colorectal cancer were 25.3% in 2004 and 54.2% in 2010 , whereas screening rates by recommended guidelines were 19.9% in 2004 and 35.5% in 2010 . in the early phase of screening , however , the introduction of colorectal cancer screening can not completely explain the differential increase in colorectal cancer incidence by subsite . fobt usually has a higher sensitivity for advanced neoplasia , including colorectal cancer and advanced colorectal adenomas , in the left vs. right colon . this explains in part the increase in the rate of distal colon cancer , but not the low increase in rectal cancer . in addition , the national cancer screening program guidelines recommend colono - scopy or double - contrast barium enema as a follow - up modality for fobt positive patients . sigmoidoscopy , which is used as a screening tool for an average - risk population in the us , is not considered as a follow - up modality in korea . therefore , there is little possibility that screening - detected cancers are more likely to be distal colon and rectal cancer . a transition in risk factors may explain the differential increase in colorectal cancer according to incidence according to subsite . in a large insurance database - based study , frequent alcohol consumption and high consumption amount were more strongly associated with risk of distal colon cancer among men and risk of rectal cancer risk among women . high body mass index ( bmi25 kg / m ) was associated with increased risk for distal colon cancer among men and for proximal colon cancer among women . in addition , frequent meat intake was associated with proximal colon cancer risk among men and risk of proximal colon and rectal cancer among women . daily alcohol consumption in korea increased from 10.6 g in 1999 to 17.3 g in 2007 among men and from 1.4 g in 1999 to 2.9 g in 2007 among women . the proportion of adult men with a bmi of 25 kg / m and was 25.1% in 1998 and increased to 35.3% in 2008 . daily per capita meat consumption was 6.6 g in 1969 and increased to 95.1 g in 2005 . in contrast , the cigarette smoking rate in the adult population decreased from 75.1% in 1992 to 43.1% in 2009 among men and from 5.1% in 1992 to 3.9% in 2009 among women . cigarette smoking has shown a stronger association with risk of rectal cancer than colon cancer . in our subsite analysis , we excluded overlapping lesions of the colon ( c18.8 ) and colon not otherwise specified ( c18.9 ) . the proportions of c18.8 did not change between 1999 and 2009 ( 1.0% for men and 0.8% for women ) , however , the proportions of c18.9 during the same period decreased from 9.8% to 5.5% among men and from 11.1% to 5.9% among women . improved accuracy in topology classification may explain in part the increase in the incidence of distal colon cancer , however , the changes exceeded the portion that might be explained by improved accuracy in topology coding . the rapid increase in colorectal cancer incidence in korea between 1999 and 2009 is mainly attributed to increases in colon cancer , especially distal colon cancer . increases in the proportion of colon cancer may be explained by a transition in risk factors for subsites and the effect of colorectal cancer screening programs . the male - to - female irrs were higher for distal colon and rectal cancer and increased between 1999 and 2009 due to more rapid changes in male colorectal cancer incidence .
purposethis study was conducted in order to demonstrate changing trends in colorectal cancer incidence according to sex , age group , and anatomical location in the korean population.materials and methodsdata from the korea central cancer registry between 1999 and 2009 were analyzed . 
 annual percent changes ( apcs ) of sex- and age - specific incidence rates for cancer of the proximal colon ( international statistical classification of diseases and related health problems , 10th revision [ icd-10 ] code c18.0 - 18.5 ) , distal colon ( c18.6 - 18.7 ) , and rectum ( c19 - 20 ) , and male - to - female incidence rate ratios ( irr ) were calculated.resultsthe age - standardized incidence rate ( asr ) of colorectal cancer was 27 ( per 100,000 ) in 1999 and increased to 50.2 in 2009 among men ( apc , 6.6% ) . 
 the asr for women was 17.2 in 1999 and 26.9 in 2009 ( apc , 5.1% ) . 
 the rectum was the most common site of cancer among both men and women during 1999 and 2009 . 
 however , the distal colon had the highest apc ( 10.8% among men and 8.4% among women ) , followed by the proximal colon ( 7.9% among men and 6.6% among women ) , and rectum ( 5.2% among men and 2.4% among women ) . 
 the proportion of rectal cancer decreased from 51.5% in 1999 to 47.1% in 2009 among men , and from 50.5% to 42.8% among women . 
 an increase in the male - to - female irr was observed for distal colon cancer and rectal cancer , whereas the irr for proximal colon cancer was stable.conclusionthe rapid increase in colorectal cancer incidence is mainly attributed to the increase in colon cancer , especially distal colon cancer , and may be explained by a transition of risk factors for subsites or by the effect of colorectal cancer screening .